Abstract: The experiment system consisting of temperature and humidity sensor, laser displacement sensor and adjustment platform was set up in this paper. The control variate method using environmental factor and displacement as the variables was used to hydrostatic leveling system (HLS) and wire position sensor (WPS), which were fixed on the same platform. The results show that the temperature is the main factor affecting the accuracy of HLS. Therefore, the more accurate result can be gotten through the temperature compensation. The humidity affects the accuracy of WPS by changing the sag of wire. Under steady condition, the maximum root mean square error of the difference value of the measuring results of HLS and WPS is 0.003 37 mm, which is in the allowable range. Therefore, HLS and WPS can work in the same system.