The paper studies on the hollow screw in X axis of boring-milling machining center. By means of the flow of the screw at different speeds and different cooling fluid, the fluid-solid-thermal coupling is researched. The heat deformation of the screw is changed with the flow rate. The optimal coolant flow rate is obtained. The curve of the optimal flow rate and the screw speed is obtained by the least square method. The results can provides a theoretical basis for the thermal error compensation of the lead screw.