In the present work, DLC coating was prepared on GCr15 bearing steel by magnetron sputtering method. The tribological behavior of GCr15 steel and DLC coating was studied at the speed range of 0.4 to 4.0 cm/s under two viscosity grades fully formulated lubricating oils (0W-20, 0W-40). The results show that viscosity of oil and sliding speed have a great effect on the DLC coating tribological properties. Compared to GCr15 steel at the speed of 0.4cm/s, there was a 41.67% reduction in the friction coefficient and 86.35% reduction in the wear rate of DLC coating in 0W-20 oil. The anti-friction and anti-wear advantages of DLC coating gradually disappear in low viscosity lubricating oil with the increase in sliding speed. The oil chain length and slip characteristics on DLC coating are two main factors that affect lubrication performance. The low viscosity lubricating oil, 0W-20, requires less energy to move and penetrate the lubricant molecules on DLC coating. This study will provide an experimental and theoretical basis for the application of low viscosity lubricating oil on DLC coating in the internal combustion engine industry.