Tribological behavior of Si3N4 ceramic/GCr15 steel components under lubrication of graphene was investigated and found that friction reduction and wear resistance of the sliding pairs were improved by 27% and 43%, respectively, after adding 0.075 wt% of graphene into the base oil. Herein, the lubrication mechanism of graphene nanoplates as oil additives was focused on to promote the practical application of graphene in hybrid ceramic bearings industry. In order to investigate the effect of oil film thickness on tribological properties, the viscosity of blended lubricating oil containing different concentration of graphene was measured and the oil film thickness between rubbing surfaces was calculated using a full numerical solution in point contacts. In addition, the rubbing surfaces were analyzed with combination of EDS and Raman technique. The results demonstrated that the viscosity of base oil and oil film thickness increased with addition of graphene. Graphene entered rubbing interface and prevented ceramic/steel pairs from mechanical contact. Lubrication mechanism including interlayer shearing, surface mending and protective film formation contributed to reduce the friction coefficient and worn scar diameter.