Semiconductor laser as the light source has many advantages such as smaller volume , but the temperature greatly influences the properties of the semiconductor laser. The temperature control must be very rigorous so that steady power of semiconductor laser is got. The temperature control system that designed according to PID control system is discussed in this paper. The precision of controlled temperature is ±0. 01 ℃, the response characteristic of the system with PID control system is better than that of the system without PID control system ,and the experiment shows that the stability of semiconductor laser power with temperature control system is better than that without temperature control system.