The development of highly active and low-cost catalysts is a challenge for the application and large-scale commercialization of proton exchange membrane fuel cell (PEMFC). In this study, a series of Pt–Ni alloy catalysts is synthesized by potentiostatic electrodeposition, and the optimum deposition parameters are determined by an orthogonal array experiment. The effect of electrodeposition parameters on the morphology, composition, and electrocatalytic activity for oxygen reduction reaction (ORR) is investigated. The Pt–Ni alloy catalyst prepared with the optimum deposition parameters of −0.35 V versus saturated calomel electrode (SCE), 50 °C for 20 min exhibits the higher ORR activity. Rapid potential cycling dealloying is also employed to modify the morphology of Pt–Ni catalysts, which results in the increase of the electrochemical surface area (ECSA) and the improvement of the ORR electrocatalytic activity. The electrochemical active surface area (ECSA) for the dealloying Pt–Ni catalyst (D-OP-sample) with the grain size of 6.2 nm is 87.0 m2 g−1. The current density and the mass activity for the electrode with D-OP-sample catalyst are 281.5 mA·cm−2 at 0.4 V and 587.9 mA· at 0.6 V, respectively.