With the rapid development of modern manufacturing of computer numerical control(CNC) machine tool, the influence of thermal factors on CNC machining accuracy is also growing. Taking XHK715 three-axis vertical machining tools with Huazhong 8 CNC control system as the main research object, the influence of thermal factors on the errors of machine tools was analyzed by measuring the errors of machine tools under different temperature conditions, the math model of thermal factors and errors influence was established, and the fitting equations of thermal error curve were calculated. Lastly, the influence law of thermal factors on the errors of machine tools is obtained, which provides effective guidance for controlling the thermal errors of machine tools.