The impacting mechanism of elastohydrodynamic lubrication (EHL) film thickness of a grease lubricated ball bearing was studied by capacitance method.The EHL film thickness was measured under different bearing speed,load,grease type and bearing ball number.The results show that the increase of bearing speed will lead to variations in temperature,although the shear stability of the tested greases is different,but the relative EHL fim thickess of all greases is reduced,which leads to more serious starvation level.The change of load only affects the EHL film thickness of the grease which has a low shear stability.When the number of bearing balls is reduced by half while the load per ball is kept the same,greases would experience less shear which leads to more serious starvation level.The research shows that the EHL film thickness of the grease lubricated ball bearing is affected by many factors,and it needs to be analyzed separately in different cases.