A novel synthesis strategy is demonstrated to prepare Mo3P/Mo nanobelts with porous structure for the first time. The growth and formation mechanism of the porous Mo3P/Mo nanobelt structure was disclosed by varying the contents of H-2/PH3 and the reaction temperature. During the hydrogen evolution reaction (HER) catalysis, the optimized porous Mo3P/Mo nanobelts exhibited a small overpotential of 78mV at a current density of 10mAcm(-2) and a low Tafel slope of 43mVdec(-1), as well as long-term stability in alkaline media, surpassing Pt wire. Density functional theory (DFT) calculations reveal that the H2O dissociation on the surface of Mo3P is favorable during the HER.