To meet the requirements of high precision, integration, and anti-interference for hazardous gas monitoring in underground coal mines, the structure of a tri-ellipsoidal multi-component gas infrared detection chamber was optimized, and an integrated CH₄-CO₂-CO gas sensor was designed. First, based on NDIR (non-dispersive infrared) measurement principle, a tri-ellipsoidal photoelectric sensing gas chamber was designed, and the optimal chamber height was obtained by introducing a reference angle combined with simulation. Second, to address the issues of signal susceptibility to interference and weak signal strength during sensor information transmission, a characteristic signal extraction and filtering-amplification circuit was designed. By integrating the excitation and signal conditioning of sensitive elements, a modular sensor hardware system was constructed to improve signal detection accuracy and antiinterference capability. Finally, a gas sensor testing and calibration platform was established to conduct experimental validation.The experimental results demonstrate that at room temperature of 25 ℃, the designed sensor can simultaneously detect CH₄, CO₂, and CO gases in the range of 0~0.40%, with a signal-to-noise ratio on the order of 10⁸, a relative standard deviation of about 0.5%, and a system response time of approximately 12 s, exhibiting excellent stability and output quality.