TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Protein: The fusion protein comprises the first area which is homologous with at least 95% of sequence of BNP and the second area which is homologous with at least 95% of sequence of HSA. The second area of the fusion protein is composed of part of the domain of HSA or the HSA after being arrayed by the domain. The fusion protein comprises the first area which is the same with the residue sequence of BNP amino acid and the second area which is the same with the residue sequence of HSA amino acid, or the function equivalent of the two areas. The function equivalent is the polypeptide obtained through replacing, deleting or adding of amino acid residue of fusion protein under the condition of not changing the property of the fusion protein. Preparation (claimed): Preparing the fusion protein of (BNP)2 and HSA by synthesizing (BNP)2 cDNA artificially; amplifying to obtain HSA cDNA from human fetal liver cDNA library by PCR; using overlapping PCR technology to connect the (BNP)2 cDNA and the HSA cDNA, without adding any connection peptide in; inserting obtained (BNP)2-HSA cDNA fusion gene into clone vector and storing it; using Pichia stipitis excretion expression vector to integrate the (BNP)2-HSA cDNA fusion gene into chromosome of parasitifer to express. Specifically it comprises (1) cloning the (BNP)2 cDNA, synthesizing (BNP)2 cDNA (195bp) artificially by Shanghai Shenggong biological engineering technology service limited corporation, and cloning it on vector pBlu2KSP, insertion site is SmaI, recipient bacterium is colon Bacillus JM 109 bacterial strain; (2) cloning the HSA cDNA, amplifying to obtain HSA cDNA from human fetal liver cDNA library by PCR, used primer is PH1 (5'-aggtcgacgatgcacacaagagtgaggttgctc-3') PH2 (5'-gccaagcttttataagcctaaggcagcttgactt-3'), PCR reaction system comprises 10 mu mol/L PH1 primer and PH2 primer, 1.5 mu l; 2.5 mmol/L dNTP, 4 mu l; 10x plaque forming units (pfu) Buffer, 5 mu l; 5U/ mu l pfu DNA polymerase, 0.5 mu l; human fetal liver cDNA library, 1 mu ; adding double distilled water to 50 mu l. Reaction program of PCR is as follows: pre-denaturation for 5 minutes at 95 degrees C; denaturation for 1 minute at 94 degrees C; annealing for 1 minute at 60 degrees C; extending for 3 minutes at 72 degrees C; circulating 30 times; extending for 10 minutes at 72 degrees C, analyzing the action production of the agar gel electrophoresis, the adding strip appearing the aim strip, purifying the 1.8kb aim segment by the PCR segment recycling agent box, the purified aim segment and the carrier pBlu2KSP are respectively double restriction enzyme cut by Sal I and Hind III, the appraising by the agar gel electrophoresis, the PCR segment recycling agent box recycles the aim segment, T4 DNA connecting enzyme connects the invert production invert Escherichia coli JM109 competent cell, coating transformation substance on the LB agar plate containing X-gal, isopropyl-beta-thiogalactopyranoside (IPTG) and 100 mu /ml ampicillin, culturing at 37 degrees C over night; picking out white colony and inoculating in the 20 ml luria brth (LB) culture media containing 100 mu /ml ampicillin, culturing at 37 degrees C over night, extracting transformed plasmid with plasmid extracting reagent box, processing PCR amplification, SalI and HindIII double enzyme-cut to verify positive clone and testing sequence of the region between the reconstruction plasmid SalI and HindIII double enzyme-cut; storing positive recon in the LB contained with 20% glycerine and freezing it at -80 degrees C, the reconstruction plasmid is named pPIC9K-(BNP)2-HSA and positive recon is named as JM109/pPIC9K-(BNP)-HSA; (3) cloning (BNP)2cDNA and HSAcDNA fusion gene: (1) PCR amplification of (BNP)2cDNA, the primer is as following: PB1 5'-gcgcgcgaattcaaaagatctccaaagatggtccaagg-3', and PB2 5'-acctcactcttgtgtgtgcatcgtgacgtctcaggaccttgc-3', the PCR reaction system comprises 10 mu mol/L PB1 and PB2 primer each 1.5 mu l, 2.5mmol/l dNTP 4 mu l, 10 x pfu Buffer 5 mu l, 5U/ mu l pfu DNA polymerase 0.5 mu l, plasmid template pBlu2KSP-(BNP)2 1ng, adding double distilled water to fill out 50 mu l; the PCR reaction program comprises 95 degrees C, pre-denaturing for 5 minutes; at 94 degrees C, denaturing for 1 minute, at 65 degrees C, annealing for 1 minute, at 72 degrees C, extending for 30s, circling 30 times; at 72 degrees C, extending for 10 minutes; (2) PCR amplification of HSAcDNA, the primer is as following: PH3 5'-gcaaggtcctgagacgtcacgatgcacacaagagtgaggt-3', and PH4 5'-cataaggcggccgcttattataagcctaaggcagcttg-3', the PCR reaction system comprises 10 mu mol/L PB3 and PB4 primer each 1.5 mu l, 2.5mmol/l dNTP 4 mu l, 10x pfu Buffer 5 mu l, 5U/ mu l pfu DNA polymerase 0.5 mu l, plasmid template pBlu2KSP-(BNP)2 1ng, adding double distilled water to fill out 50 mu l; the PCR reaction program comprises 95 degrees C, pre-denaturing for 5 minutes; at 94 degrees C, denaturing for 1 minute, at 65 degrees C, annealing for 1 minute, at 72 degrees C, extending for 3 minutes, circling 30 times; at 72 degrees C, extending for 10 minutes; (3) fusing (BNP)2cDNA and HSAcDNA by overlapping PCR technology: separately diluting the PCR amplified product of (BNP)2 and the PCR amplified product of HSA for 10 times, then mixing them by ratio 1:10, taking them as template, adding 2x Pfu Buffer 25 mu l into 50 mu l reaction system, the mixed template is 25 mu l. The PCR reaction program comprises 95 degrees C, pre-denaturing for 5 minutes; at 94 degrees C, denaturing for 1 minute, at 65 degrees C, annealing for 1 minute, at 72 degrees C, extending for 4 minutes, circling 15 times; at 72 degrees C, extending for 10 minutes; taking the PCR primer as template, adding 10 mu mol/l primer PB1 and PH4 each 1.5 mu l into 50 mu l reaction system, 2 x Pfu PCR MasterMix x 25 mu l, template 4 mu l; adding double distilled water to fill out 50 mu l. The PCR reaction program comprises 95 degrees C, pre-denaturing for 5 minutes; at 94 degrees C, denaturing for 1 minute, at 65 degrees C, annealing for 1 minute, at 72 degrees C, extending for 4 minutes, circling 35 times; at 72 degrees C, extending for 10 minutes; analyzing reaction product by agarose gel electrophoresis, target belt appears in loading swimming course, recovering kit with PCR segment to purify 2kb target segment. The purified overlapped PCR product and carrier pBlu2KSP are cut by EcoRI and NotI double enzyme, identified by agarose gel electrophoresis, recovering kit with PCR segment, HSAcDNA gene and carrier pBlue2Ksp. Connecting two recovering segments with T4DNA connecting enzyme, connecting primer converted coli bacillus JM109 competent cell, invert is collated on LB agar plate containing X-gal, IPTG and 100 mu /ml penbritin, culturing and staying over night at 37 degrees C, selecting white colony, inoculating it to 20ml LB culture medium containing 100 mu /ml penbritin, culturing and staying over night at 37 degrees C, extracting converted plasmid with plasmid extracting kit, amplifying it with PCR, identifying masculine cloning with EcoRI and NotI double cut enzyme, and taking DNA sequence test to the double cut enzyme position region of recombined plasmid EcoRI and NotI, storing masculine recombined plasmid in LB containing 20% glycerine, cooling it at -80 degrees C, naming recombined plasmid as pBlu2DSP-(BNP)2-HSA, naming masculine recombined plasmid as JM109/pBlu2KSP-(BNP)2-HSA; (4) building the enzymes expression system of the fusion protein (BNP)2-HSA, adopting a freezing JM109/pBlu2KSP-(BNP)2-HSA to transferring on 20ml of LB culture medium containing 100 mu /ml ampicillin, culturing for night under 37 degrees C, extracting the plasmid using the plasmid extracting agent box, the extracted the pBlu2KSP-(BNP)2-HSA and the enzymes expression carrier pPIC9K are respectively double restriction enzyme cut by the EcoRI and NotI, appraising by the agarose gel electrophoresis, using PCR segment recycling agent box to recycle (BNP)2-HSA gene and the carrier pPIC9K, connecting the two recycling segments by T4 DNA, the connection production is transformed into Escherichia coli competent cell, the invert is printed on the LB agar plate containing 100 mu /ml ampicillin, culturing for night under 37 degrees C, Picking out grown colony and inoculating it to 20 ml LB culture media contained with 10 mu /ml ampicillin, culturing it at 37 degrees C one night, extracting plasmid with plasmid extracting reagent box, processing PCR amplification, EcoRI and NotI double enzyme-cut to test positive clone, storing positive recon in the LB contained with 20% glycerine and freezing it at -80 degrees Cm reconstruction plasmid is named pPIC9K-(BNP)2-HSA and positive recon is named as JM109/pPIC9K-(BNP)-HSA; extracting the plasmid in JM109/pPIC9K-(BNP)2-HSA, processing SalI single enzyme-cut, recovering with DNA glue recovering reagent and then electrically shocking to transform Pichia GS115, extracting and reconstructing Pichia genome DNA, verifying PCR amplification, and positive reconstruction sub-name is GS115/pPIC9K-(BNP)2-HSA; (5) expression of fusion protein (BNP)2-HSA: inoculating GS115/pPIC9K-(BNP)2-HSA to a 50 ml triangular flask filled with 10 ml BMGY by the speed rate of 250 rpm and culturing at 30 degrees C for 24 hours, centrifugally collecting thallus and then inoculating the thallus to a 50 ml triangular flask filled with 3 ml BMMY, adding formaldehyde once per 24 hours till final concentration is 2%, inducing for 3 days, centrifugally collecting supernatant and testing for Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE), and verifying the BNP and HSA immunity source performance of fusion protein (BNP)2-HSA molecule by Western hybridization. The host cell is bacteria, insect cell, animal cell or plant cell, preferably yeast, i.e. Pichia BS115 and KM71.