NOVELTY - An engineered Escherichia coli obtained by amplifying acetyl-coenzyme A carboxylase gene, sulfatide enzyme gene, acyl-coenzyme A reductase gene and fatty aldehyde decarboxylase gene, performing double digestion of target fragment and pronucleus expression vector, mixing the vector with gene fragment, ligating the fragment, applying thermal shock to E.coli cell, screening the positive clone and extracting plasmid DNA, performing enzyme digestion, applying thermal shock to E.coli and knocking fadE gene of E.coli, is new.    USE - The engineered E.coli is used for preparing biological gasoline, preferably 8-12C alkane (claimed).    DETAILED DESCRIPTION - An engineered Escherichia coli obtained by amplifying acetyl-coenzyme A carboxylase gene, sulfatide enzyme gene, acyl-coenzyme A reductase gene and fatty aldehyde decarboxylase gene by PCR, recovering target fragment through gel extraction kit, performing double digestion of target fragment and pronucleus expression vector pET-30a(+) or pACYCDuet-1, performing gel extraction of vector fragment, mixing the vector with gene fragment in mole ratio of 1:2-4-5, adding T4 DNA ligase, ligating the fragment at 4-7 degrees C for 15-30 hours, applying thermal shock to E.coli DH5 alpha competent cell at 38-42 degrees C, culturing the cell, screening the positive clone, processing the positive clone to extract plasmid DNA, performing enzyme digestion and sequence analysis, applying thermal shock to E.coli BL21 and knocking fadE gene of E.coli to obtain engineered E.coli, is new. An INDEPENDENT CLAIM is included for method for preparing biological gasoline, which involves inoculating the above-mentioned engineered E.coli into M9 liquid culture solution containing kanamycin and chloramphenicol in the ratio of 1-2:100-130, culturing the solution at 35-37 degrees C with speed of 225 revolution per minute (rpm) until the optical density at 600 nm is 0.6-0.8, adding inducer isopropyl- beta -D-thio-galactoside (IPTG) (0.1-0.2 mmol/l) to the solution, inducing the target protein to over express, culturing the solution continuously at 28-30 degrees C for 18-24 hours with the speed of 225 rpm, centrifuging the culture liquid and obtaining supernatant, extracting the supernatant using n-hexane and removing hexane under reduced pressure evaporation to obtain biological gasoline.