Objective In order to improve the hardness of single electroless plating Ni-P coatings, SiO2 particles were incorporated into the plating to form Ni-P-SiO2 composite coating. Methods The effects of plating temperature, concentration of SiO2 particle and temperature of heat treatment on the structure and hardness of the deposits were analyzed. Results It was found that amorphous Ni and high content of SiO2 phase were detected in the composite coating. With the increase of plating temperature and concentration of SiO2 particle, the coating became more homogeneous and dense, and exhibited increased hardness till 355HV. However, the coating surface was rough and porous, and the hardness decreased when the plating temperature was above 80 ℃ and the particle concentration was higher than 10 g/ L. After heat treatment, the coating was transformed to crystalline and the coating hardness was raised. The Ni3P phase appeared when the coating was heated at 300 ℃ for 1 h. Conclusion When the temperature was 80 ℃ and the concentration of SiO2 particle was 10 g / L , the performance of composite coating was the best. The microhardness of coating raised with the increasing temperature of heat treatment.