Abstract: As the support mechanism of linear motor, the linear-motor rolling-guide stage is often used in high precision linear motion. When working, the stage suffers a variety of forces such as magnetic thrust, gravity in movement, which will result in elastic deformation and space position error of stage. In this paper, the relationship between the deformation of balls and the displacement of linear-motor rolling-guide stage under external loads is analyzed by mechanical modelling and the calculating model of space position accuracy of the stage is established on the basis of Hertz contact formula. By using the calculating model the influences of the mass and the barycenter position of stage, installation position and mass of workpiece, installation height of armature, acceleration of stage and preloading deformation of balls on the space position accuracy of the stage are studied. When the mass of workpiece is small, the effect of the mass and installation positon of the workpiece on its space position accuracy is the same as the effect of the mass and barycenter of stage itself, that is, the stage moves linearly and in the same direction with the increasing of deviation of the installation positon of workpiece or the barycenter position of stage and moves linearly in three directions of space with the increasing of mass of workpiece or stage itself. When the mass of workpiece is large, the space position of stage will change nonlinearly with the increasing of mass of workpiece. When the installation height of armature is not the same as the height of barycenter of stage, it moves linearly in the opposite direction with acceleration increasing and the farther the distance of the two is, the greater the proportionality coefficient becomes. The increasing of preloading deformation of balls can improve the space position accuracy of stage but also increase the balls' maximum contact stress.