In order to obtain a narrow linewidth laser with good short-term frequency stability, a free running laser is locked in a Fabry-Pérot (F-P) reference cavity which has the characteristics of vibration isolation, constant temperature and high fineness. To reduce the influence of temperature on laser frequency stability, the F-P cavity is generally made of glass material with ultralow-expansion (ULE) coefficient. There is a special temperature point called inflection point temperature for ULE glass, and the ULE coefficient of glass is almost zero under such special temperature. For the inflection point temperature is always higher or lower than the room temperature, we design an active temperature control equipment which can control the F-P cavity temperature in the range of -5-40 ℃ in high vacuum environment, with a temperature fluctuation less than ±0.005 ℃ in one day. The temperature control equipment is employed to ULE F-P cavity system with the working wavelength of 729 nm, and the average linear frequency drift is within 100 mHz/s when the reference cavity temperature is controlled near the inflection point temperature of 17.3 ℃.