The reaction mechanism of electroless nickel plating is analyzed emphatically. The reaction step of reduction between activating and electroless plating is added in this article. The process for electrodes nickel plating on diamond powder is optimized by orthogonal experiment. The most optimal parameters are nickel sodium 26 g/L, sodium hypophosphite 22 g/L, sodium citrate 8 g/L, sodium formate 8 g/L and pH 9~10. The morphology, composition and phase structure of the Ni-P coating are analyzed by the SEM, EDX and XPS techniques. The results show that the phosphorus mass fraction of the compact-structure Ni-P coating obtained under the optimal conditions on diamond powder is 7.78%, and belonging to a middle-phosphorous coating. The hardness, wear resistance and corrosion resistance of middle phosphorous coating are moderate and the magnetic of middle phosphorous coating is small, which is conductive to sebsequent electroplating.