The monolithic non-planar ring cavity is applied to produce single frequency laser , while the laser frequency fluctuates with temperature of laser crystal. An apparatus to control the temperature of the laser crystal in order to stabilize the laser frequency is designed. By combining single-chip microcomputer and PID module , the temperature is stabilized within±0. 01 ℃in 32 ℃, and the laser frequency fluctuates within 50MHz correspondingly. Furthermore , the frequency tuning of the single frequency laser was also studied by adjusting the temperature of the crystal . In this temperature control system ,more stabilized temperature is realized effectively.