The invention relates to a chemical Ni-P plating technique on the surface of magnesium alloy which takes nickel sulfate (NiSO4, 6H20) as the main salt. The technique process is as follows, ultrasonic cleaning, alkali cleaning, acid cleaning, activation, and chemical nickel phosphorus plating (water cleaning is employed among steps), dispensations of plating solution are NiSO4, 6H2O (20 grams per liter), HF (40%, 12 milliliter per liter), Na3C6H5O7, 2H2O (20 grams per liter), NH4HF2 (10 grams per liter), NH3, H20 (25%, 30 milliliters per liter), and NaH2PO2, H2O (20 grams per liter), and the plating temperature is 88 +-2 DEG C. The plating speed on the surface of magnesium alloy is 20 micrometers per hour, and the plated rigidity is 300-500 HV. The invention is low in cost and simple in plating solution dispensation, and is applicable to the magnesium alloy in Mg-Al-Zn series (AZ series).