The PbSe mid-infrared detector is the core component of the CO gas detector and its response rate varies with temperature. Accurate temperature control of the mid-infrared detector can effectively improve the stability of the system and signal-to-noise ratio. Firstly, the temperature characteristics of PbSe detector are analyzed. According to the design index of CO detector, the high stability requirements of temperature control system are put forward. Then the working principle of thermoelectric cooler (TEC) is introduced. The temperature control scheme based on temperature and humidity control chip ADN8830 is proposed, and the corresponding input bridge circuit, TEC power amplifier circuit and PID compensation circuit are designed. Finally the experimental test system is built according to the design scheme and tested at room temperature. The test results show that, when the temperature control system is applied in the atmospheric CO concentration detection instrument, it can enter a stable state within 30 s, and the temperature fluctuation within 1 min is less than 0.02℃, which is superior to the requirement that the temperature fluctuation required for the 1 ppm accuracy index of the CO detector is not more than 0.1℃.