The friction-enhancing performance of Ni-P/Diamond composite coating critically depends on diamond particle bonding strength and uniform distribution. Herein, a metastable Ni-P/Diamond coating featuring high bond strength and uniform diamond distribution was successfully developed. The current study reveals the regulation of the bond strength and distribution density of diamond particles in Ni-P/Diamond composite coating, as well as the regulation of the microstructure and properties of the composite coating. The main phases of the metastable Ni-P/Diamond composite coating were amorphous, diamond and Ni. The Ni-P/Diamond composite coating has diamond particles embedded in a size of 1/2–2/3 of their particle size, and the surface distribution density of diamond particles was 25 %. The static coefficient of friction of the Ni-P/Diamond composite coating was 0.58. The as-prepared friction-enhancing spacer samples were run in a 560 kW engine for 500 h and no delamination of diamond particles from the Ni-P/Diamond composite coating was observed.