The invention relates to a preparation method of Ni-W-P graded alloy. The preparation method is characterized in that an electrolyte of the Ni-W-P alloy comprises the following components according to concentrations: 20-100 g/L of nickel salt, 10-60 g/L of tungstate, 30-60 g/L of conducting salt, 15-40g/L of a dispersing agent, 10-30 g/L of citric acid, 5-40 g/L of phosphorous acid and 10-30 g/L of boric acid; the preparation method comprises the following steps: immersing workpieces after pretreatment in the electrolyte of 45-75 DEG C, adopting the linear sweep voltammetry or cyclic linear sweep voltammetry for scanning at the speed of 0.1-100 mV/s within the range from minus 1.3 V to minus 0.5 V, and adjusting the sedimentary dynamic states of different ions by adjusting the deposition potential, so as to obtain the Ni-W-P graded alloy. According to the preparation method of the Ni-W-P graded alloy, the Ni-W-P graded alloy coating prepared by adopting the preparation method has a single-layer or multi-layer graded structure and contains amorphous phases, the microhardness can reach 500-1150 Hv, the corrosion resistance and wear resistance of the coating are obviously improved, and the preparation method has a potential application prospect.