In the working process of numerically-controlled machine tool, the generation of heat by friction between the guide rail and the workbench will cause the thermal deformation under the high temperature, which impacts on the machining accuracy of machine tool. Through the finite element modeling for the guide rail of machine tool by the ANSYS software, the thermal characteristics is simulated in the process of guide rail, then the main factors of thermal deformation is analyzed, finally the corresponding measures focusing on the error compensation is proposed.