The theory of joint surface was used to analyze the force on the column of vertical machining center. The joint between the column and other parts of the machine tool was divided into fixed joint surface and moving joint surface. The fixed joint surface had large contact stiffness, it was unnecessary to consider its stress and deformation. The normal pressure on the fixed joint surface was simplified as the uniform force,combined with the main machining process of the machine tool, the cutting force was simplified into three orthogonal forces and rotation moment around the axis of the spindle. No relative motion after the fixed joint surface was loaded was taken as the principle, the working load of the threaded joint and the uniform load on the joint surface were analyzed. For the moving joint surface composed of column and slide block,according to the pressure theory of the joint surface, the deformation and normal pressure of the joint surface were treated as a linear function along the joint surface. Based on the established equilibrium conditions,the load distribution functions of different parts on the main and secondary joint surfaces were obtained.