Maximize the Pt utilization with high durability and efficient mass transport is crucial on the electrocatalyst design for the practical low-temperature fuel cell applications. In this work, we designed an ultrafine PtCo alloy nanoparticles distributed uniformly on phosphorus and sulfur co-doped hierarchical porous carbon nitride (PtCo/P,S-HPCN), synthesized via hydrothermal treatment, pyrolysis, and chemical reduction. The heteroatom-doped carbon nitride framework exhibits superior chemical stability compared to conventional carbon materials, while its hierarchical porous structure facilitates uniform dispersion of ultrafine PtCo nanoparticles (∼1.8 nm) and accelerates reactant transport. Synergistic effects from graphitic/pyridinic nitrogen species, P/S doping, and Pt–Co alloying modulate the electronic structure of Pt, optimizing *OOH binding and enhancing ORR kinetics. The optimized catalyst delivers excellent performance in acidic media, achieving a high half-wave potential (0.88 V vs. RHE), a mass activity of 0.91 mA µgPt⁻1, and a specific activity of 2.37 mA cmPt⁻2 at 0.85 V. Remarkably, it retains 73% of its initial mass activity and loses only 11 mV in half-wave potential after 5000 durability cycles. In practical PEMFC tests, the PtCo/P,S-HPCN cathode achieves a peak power density of 0.42 W cm⁻², surpassing commercial 40 wt% Pt/C. This study demonstrates a promising strategy for designing durable, low-Pt and high activity catalysts for PEMFC applications.