Abstract: To construct contact stiffness of the ball linear guides model,mechanics and deformation of the contact surface between the ball and raceway based on Hertz contact theory were analyzed. The change of ball's contact angle under loading was considered. The relationship of contact force and elastic deformation of the single ball was deduced. From this,The relationship of external load and elastic deformation of ball linear guides was deduced. Tooking the NSK ball linear guides as objects,the simulation of the proposed model was anylazed. The guide's critical load under different preloads were calculated. The change of guide's contact stiffness were analyzed when the external load was larger than the critical load and less than the critical load. By comparing the data on the NSK official website,the proposed model and the theoretical analysis are reasonable.