The bearing FEM model was built according to the parameters of 6003 deep groove ball bearing，and the stress and the deformation of the bearing were computed based on static method. According to the cyclical nature of the bearing rotation, the changes of the stress of rolling elements and the changes of the bearing stiffness were analysed during one roll period of the bearing. The results show that the stress of rolling elements and the bearing stiffness change periodically when the bearing is rotated, and the stress of rolling elements and the bearing stiffness are the largest when one rolling element is located in the direction of the radial force.