The temperature characteristics of avalanche voltage of single photon detector SPAD were analyzed. It’s concluded that the avalanche voltage of SPAD variation with temperature is about 0.7 V/°C. The constant temperature control circuit was designed to ensure the normal operation of SPAD. From the perspective of the optimal temperature control strategy, MAX1978 temperature control chip design circuit was chosen to realize the SPAD temperature constant. The working principle and main component of constant temperature control system were introduced. Through the experiment of constant temperature control circuit to verify the feasibility of the circuit, constant temperature control circuit can make the SPAD working environment temperature constant at 0.06°C in 1 minute, the speed and accuracy of temperature control can meet the requirement of SPAD temperature constant, and ensure the normal work of the single photon detector SPAD, so that the single photon detector SPAD has better performance.