How to optimize and regulate the distribution of phosphoric acid in matrix, and pursuing the improved electrochemical performance and service lifetime of high temperature proton exchange membrane (HT-PEMs) fuel cell are significant challenges. Herein, bifunctional poly (p-terphenyl-co-isatin piperidinium) copolymer with tethered phosphonic acid (t-PA) and intrinsic tertiary amine base groups are firstly prepared and investigated as HT-PEMs. The distinctive architecture of the copolymer provides a well-designed platform for rapid proton transport. Protons not only transports through the hydrogen bond network formed by the adsorbed free phosphoric acid (f-PA) anchored by the tertiary amine base groups, but also rely upon the proton channel constructed by the ionic cluster formed by the t-PA aggregation. Thorough the design of the structure, the bifunctional copolymers with lower PA uptake level (<100%) display prominent proton conductivities and peak power densities (99 mS cm⁻¹, 812 mW cm⁻² at 160 °C), along with lower PA leaching and higher voltage stability, which is a top leading result in disclosed literature. The results demonstrate that the design of intermolecular acid–base-pairs can improve the proton conductivity without sacrificing the intrinsic chemical stability or mechanical property of the thin membrane, realizing win-win demands between the mechanical robustness and electrochemical properties of HT-PEMs.