A kind of polyimide (PI) copolymer was synthesized via a one step polycondensation using benzophenone-3, 3’, 4, 4’-tetracarboxylic acid dianhydride (BTDA), toluene diisocyanate (TDI) and 4, 4’-methylenebis (phenyl isocyanate) (MDI). The chemical structures of the obtained copolymers were characterized by FT-IR, Roman and 1H-NMR. The influencing factors were investigated by ortho gonal test, and the optimized conditions were obtained: reaction temperature is 80 ℃, the mole ratio of BTDA and -CNO is 1∶1.05, the feed rate of -CNO is 14 s/d～16 s/d, the mass of catalyst is 0.005 g. As evidenced by the variance analysis, the mole ratio of BTDA and -CNO is the significant factor.