The invention belongs to a surface treating method of magnesium alloys, in particular relates to a method for improving the surface hardness of the magnesium alloys, namely an alloy layer is coated on the surface of the magnesium alloy, and the steps includes alkali cleaning and degreasing, surface conditioning, activation and chemical plating alloy layer. The alloy player is a Ni-P-V alloy layer and the plating bath contains the following materials: NiSO4, C6H5Na3O7, NH4HF2, and HF with the volume concentration of 40 percent, NaH2PO2 and soluble salt of the highest vanadium. The treating method has simple technology, is environment-friendly and can effectively improve the surface micro-hardness of magnesium alloys, and simultaneously, the method can reduce the demands for working condition, greatly shortens working time, and improves production environment and production efficiency.