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Hydrogen generated by proton exchange membrane (PEM) electrolyzer holds a promising potential to complement the traditional energy structure and achieve the global target of carbon neutrality for its efficient, clean, and sustainable nature. The acidic oxygen evolution reaction (OER), owing to its sluggish kinetic process, remains a bottleneck that dominates the efficiency of overall water splitting. Over the past few decades, tremendous efforts have been devoted to exploring OER activity, whereas most show unsatisfying stability to meet the demand for industrial application of PEM electrolyzer. In this review, systematic considerations of the origin and strategies based on OER stability challenges are focused on. Intrinsic deactivation of the material and the extrinsic balance of plant‐induced destabilization are summarized. Accordingly, rational strategies for catalyst design including doping and leaching, support effect, coordination effect, strain engineering, phase and facet engineering are discussed for their contribution to the promoted OER stability. Moreover, advanced in situ/operando characterization techniques are put forward to shed light on the OER pathways as well as the structural evolution of the OER catalyst, giving insight into the deactivation mechanisms. Finally, outlooks toward future efforts on the development of long‐term and practical electrocatalysts for the PEM electrolyzer are provided. [ABSTRACT FROM AUTHOR]