Abstract: Non-dispersive infrared (NDIR) combustible gas concentration detectors can effectively detect gas leaks in mines to prevent gas leakage during the mining process and ensure the safe production of coal mines. In order to improve the detection accuracy, sensitivity, and robustness of the NDIR type combustible gas concentration detector, based on the pyramid beam splitter matrix, the internal optical structure of the sensitive element is newly designed. The multi-frequency signal superposition technology is used to modulate the infrared light source. The 4-channel combustible gas concentration redundancy algorithm based on the linear frequency modulation Z-transform (CZT) is de signed. Also, the spectral refinement analysis is contacted through the characteristic frequency band of the signal to give the combustible gas concentration detection results and the confidence level of the detection results. The experiments show that the effective detection concentration of the detector is 10%-90% of the lower explosive concentration limit (5% of the lower explosive concentration limit of methane), and the confidence level of the detection results is 0.014 ×10^-6. The limit measurement concentration of the detector for combustible gases can reach 0.5 ×10^-6, and the confidence level of the detection results is 0.01 ×10^-6. Under the unfavorable condition that the detector optical window is blocked by 2/3, the detector can still detect normally, and the confidence level of the detection results can still reach 0.01 × 10^-6. Under the extreme environment of 85% humidity and 100 mg/m³ dust concentration, the detector can still detect effectively and the confidence level of the detection result can still be at 0.01×10^-6 level. The developed combustible gas concentration detector increases the detection sensitivity to the 0.01× 10^-6 level and can give the confidence level of the detection results. The designed optical circuit structure enables the detector to achieve a high-precision detection of combustible gases even in extreme environments with high humidity and dust. It effectively improves the detection accuracy, sensitivity, and robustness of the detector, making it adaptable to the harsh environment of coal mines. It can achieve very early detection of coal mine gas leaks, and can also reduce its maintenance cost.