TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Claimed): Preparation of (I) comprises either uniformly mixing aromatic diamine with 2,3,3',4'-biphenyl tetracarboxylic diandhydride and 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride for performing polymerization reaction to obtain homogeneous-phase solution, and then adding acetic anhydride and pyridine to mix uniformly to perform chemical imidization reaction or uniformly mixing the aromatic diamine with the 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride for performing the polymerization reaction to obtain the homogeneous-phase solution after the reaction, and then adding the acetic anhydride and the pyridine to mix uniformly to perform the chemical imidization reaction. Preferred Components: The aromatic diamine comprises 4,4'-diamino diphenyl ether, 3,4'-diamino diphenyl ether, 1,4-bis(4-amino phenoxyl) benzene, 1,3-bis(4-amino phenoxyl) benzene, 1,3-bis(3-amino phenoxyl) benzene, 1,4-bis((4-amino-2- trifluoromethyl) phenoxyl) benzene, 2,2- bis((4-amino phenoxyl) benzene) propane, 2,2-bis((4-amino phenoxyl) benzene) hexafluoropropane or 2,2'-bis trifluoromethyl-4,4'-biphenyl diamine. (A) has a: molar ratio of 2,3,3',4'-biphenyl tetracarboxylic diandhydride to the 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride is 0:100-100:1, preferably 40:60-80:20; molar dosage of the 2,3,3',4'-biphenyl tetracarboxylic diandhydride is not 0; proportion of the total molar dosage of the 2,3,3',4'-biphenyl tetracarboxylic diandhydride and the 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride to the molar ratio of the aromatic diamine is 1:(0.95-1.00), preferably 1:(0.99-1.00); proportion of the total molar dosage of the 2,3,3',4'-biphenyl tetracarboxylic diandhydride and the 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride to the acetic anhydride is 1:(2-10), preferably 1:3; proportion of the total molar dosage of the 2,3,3',4'-biphenyl tetracarboxylic diandhydride; and proportion of the total molar dosage of the 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride to the pyridine is 1:(2-8), preferably 1:3; and (B) has a: molar ratio of 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride to the aromatic diamine is 1:(0.95-1), preferably 1:(0.99-1); molar ratio of the 2,3,3',4'-diphenyl ether tetracarboxylic diandhydride to the acetic anhydride is 1:(2-10), preferably 1:3; and molar ratio of the 3,3',4'-diphenyl ether tetracarboxylic diandhydride to the pyridine is 1:(2-8), preferably 1:3. Preferred Method: In the method, the polymerization reaction process is carried out at 0-35 degrees C, preferably 15-25 degrees C for 10-30 hours, preferably 24 hours, and chemical imidization reaction process is carried out at 0-35 degrees C, preferably 15-25 degrees C for 10-30 hours, preferably 24 hours. The polymerization is carried out in an organic solvent comprising N-methyl pyrrolidone, m-cresol (both preferred), N,N-dimethyl formamide, N,N-dimethyl acetamide, dimethyl sulfoxide and gamma -butyrolactone, the dosage of the solvent is determined, and the mass percentage of the solid in the reaction system is 10-30%, preferably 15-20%.