Abstract: Ni-P/diamond composite coatings were prepared onto low carbon steel substrates by the composite electroplating process at temperature of 60℃.Diamond particles were embedded uniformly in the Ni-P alloy matrix with low P content while some diamond particles projected from the surface of Ni-P alloy coating. In dry condition, when the diamond content in Ni-P alloy matrix was in the range of 22%±5%, Ni-P/diamond composite coating had the maximum static friction coefficient about 0.72, and the static friction coefficient increased with the increasing grain size of diamond particles. Especially in oil or grease lubricating condition, the static coefficient of Ni-P composite coatings remained around 0.5. As compared to the conventional pair of steel/steel, the special surface texture design of Ni-P/diamond composite coating greatly improved the mechanically inter-lock effect on the counterpart, showing a 200% to 300% increase of friction force, which could be potentially applied in the driving system of modern machinery equipment.