In order to prolong the working life of mechanical seals,the micro crystalline diamond (MCD),nano crystalline diamond (NCD) and micro/nano crystalline diamond (MNCD) films with excellent wear resistance and low friction coefficient were deposited on the working faces of silicon carbide mechanical seals by chemical vapor deposition method.The results of Raman spectrum analysis show that the thickness of asdeposited MCD,NCD and MNCD films is all about 30~50 μm.The Raman spectrum of MCD film shows distinct peak of crystalline diamond,while the G and D peaks representing graphite and amorphous carbon are presented in the Raman spectra of NCD and MNCD films.The subsequent polishing properties of MCD,NCD and MNCD coated mechanical seals were comparatively studied by the plane polishing experiments.The experimental results indicate that the MNCD coating exhibits higher polishing efficiency and excellent wear resistance,showing better functional performance compared with the MCD and NCD films,which is more suitable to be deposited on the mechanical seals to improve their wear resistance.