In this paper, binary copolymerized polyimide precursors polyamic acid PAA-A and PAA-B were first synthesized using pyromellitic dianhydride (PMDA) with 4,4′-diaminodiphenyl ether (ODA) and p-phenylenediamine (PPDA), respectively. The corresponding polyimides PI-A and PI-B were then obtained via thermal amide cyclization. Subsequently, block copolymerized polyamide acid PAA-AB was obtained through the reaction of PAA-A and PAA-B, and block copolymerized polyimide PI-AB was also obtained through thermal amide cyclization. Finally, the chemical structure, aggregation structure, and cross-sectional morphology of the three PI were characterized, and their mechanical properties, dielectric properties, electric strength, and electronic structure were tested and analyzed. The results show that the introduction of the third monomer PPDA and ODA does not induce the formation of defects in PI-AB. Furthermore, due to the alteration in chemical structure, the molecular chain spacing of PI-AB slightly increases compared to that of PI-A, which results in a decrease in its glass transition temperature. The electric strength of PI-AB is 6.18% higher than that of PI-A. The dielectric loss factor of PI-AB remains below 0.07 in the frequency range. Moreover, the band gap of PI-AB is wider than that of PI-A, making electron excitation more difficult, which demonstrates that PI-AB has superior insulating properties.