AbstractA Co‐based zeolitic imidazolate framework (ZIF‐67) derived catalyst with ultrafine CoPt nanoalloy particles is designed via a two‐step space confinement method, to achieve a robust oxygen reduction reaction (ORR) performance for proton exchange membrane fuel cell (PEMFC). The core–shell structure of ZIF‐67 (core) and SiO2(shell) is carefully adjusted to inhibit the agglomeration of Co nanoparticles. In the subsequent adsorption−annealing process, the in situ formed graphene shell on the surface of Co nanoparticles further protects metal particles from coalescence, leading to the ultrafine CoPt nanoalloy (average diameter is 2.61 nm). Benefitting from the high utilization of Pt metal, the mass activity of CoPt nanoalloy catalyst reaches 681.8 mA mgPt−1at 0.9 V versus RHE according to the rotating disk electrode test in 0.1mHClO4solution. The CoPt nanoalloy‐based PEMFC provides a high maximum power density of 2.22 W cm−2(H2/O2) and 0.923 W cm−2(H2/air). Simultaneously, it shows good stability in the long‐time dynamic test at low humidity, due to the robust CoPt@graphene core–shell nanostructure. This work provides a viable strategy for designing Pt‐based nanoalloy catalysts with ultrafine metal particles and high stability.