The trace CO concentration detection system based on tunable diode laser absorption spectroscopy (TDLAS) technology presents low detection accuracy owing to interference from various environmental factors. Temperature fluctuations affect the responsivity and dark current of the photodetector, thus causing a drift in the detector's output signal, which consequently affects the accuracy of CO detection. Hence, a high-precision constant-temperature control system with a wide temperature range is designed in this study. The effect of temperature on the photodetector's output signal is analyzed based on both the responsivity and dark current of the photodetector. Subsequently, a high-precision constant-temperature control drive module is designed using a relay feedback self-tuning proportional-integral-derivative adjustment algorithm, dual-channel voltage acquisition, and an improved comprehensive Kalman filter algorithm. Experimental results show that this high-precision constant-temperature control system can achieve a temperature-control accuracy of ±0.005 °C in both high- and low-temperature environments.