Abstract: Thermoelectric cooler (TEC) had an extensive prospect for the application of refrigeration system for laser diode (LD) for its advantage such as small in size, easy to control and so on. But it was necessary to ensure the match between the cooling power of TEC and the thermal power of the target;otherwise it would lead inadequate cooling or excessive power dissipation. In this paper, a high precision thermostat system with TEC for laser diode was designed. In this system, the cooling power of TEC was determined by the thermal load of LD, proportional-integral-derivative (PID) control method was used to optimize the parameters of the thermostat system. An experiment was executed to verify the design. The experimental results showed that the work temperature of LD could be controlled between 5℃ and 41℃ with a control accuracy of 0.05℃ and the steady state error was small. The system could be a good solution for the high-precision wavelength testing.