A facile two-step method is developed for large-scale synthesis of chemically ordered Pt3Co nanoparticles (NPs) as a high-performance catalyst for hydrogen evolution reaction. Due to the NaCl-matrix as dispersing media avoids the severe aggregation during the high-temperature annealing process, the resulting Pt3Co NPs are pure and well crystallized with narrow size distribution. Furthermore, the chemically ordered Pt3Co NPs exhibit excellent HER property in acidic solution. Our methodology can be also applied to synthesis of other Pt-based NPs.