Abstract: To enhance the bonding strength between diamond and matrix, Ni-Co-P alloy is deposited onto the diamond surface by using electroless plating. The influence of different depositing parameters on the performance of the coated layer is studied by scanning electron microscope and X-ray diffraction. Results show that the best formula is cobalt chloride 11.8 g/L, nickel sulfate 8.7 g/L, sodium hypophosphite 18 g/L, sodium citrate 50 g/L, ammonium sulfate 60 g/L and addition agent 0.1 g/L and that the best parameters are solvent temperature 76 ℃, pH value 9.0 and coating for 2 h. At such formula and parameters the spherical protrusions are formed and strongly bonded to the diamonds. It is also found that if the coatings are heated at 400 ℃ or higher, there will precipitate stable phases such as Ni, Ni₃P, CoP and Co₂P.