The contact characteristics of the ball bearing coated with DLC in MEMS were studied theoretically.According to the contact of the microball bearing,a FEM model for the microball and the raceway coated with DLC was built.The effects of the elastic modulus and thickness of DLC film and the material and diameter of microball on the contact characteristics of microball bearing were investigated.The results show that the high elastic modulus and thick DLC film can reduce the maximum radial tensile stress along the raceway surface and the maximum shear stress along the interface,whereas increasing the maximum contact pressure.The maximum von Mises stress along the axial direction and the stress gradient along the interface in the bearing can be reduced by decreasing the elastic modulus or increasing the thickness of the DLC film.The larger diameter 440C stainless steel microball can improve the contact characteristics of microball bearing.