Home- and copolyimides with high molecular weight could be synthesized from three dianhydrides and three diamines following two different one-step methods. Solubility behavior with structural effect, viscosity, kinetics of solution imidization, synthesized method, mechanical and thermal properties, and effect of azeotroping agent are discussed. Results indicate that homo- and random copolyimides were only prepared from a one-step method; on the other hand, copolyimide with different arrangement, such as random, block, and alternating, could be synthesized by a modified one.