To improve the precision of the infrared sensor, the chamber structure, circuit and data processing was optimized. The chamber structure of the infrared gas sensor was redesigned and optimized by the experiments and optical simulation. Three differential amplifier circuits were chosen to eliminate the system's noise, and the secondary difference look-up table was used to process the data, and a new infrared methane sensor was designed by those measures. The experiments were performed to obtain the new sensor′s performance in the volume fraction 0%-3% of the methane. Results showed that the response time has been reduced to 20 s, the detection sensitivity was also improved, and the detection error was controlled within ±0.04%. After comparing the similar products at home and abroad, it is clear that this new designed sensor exhibits enhanced performances including higher detection sensitivity, lower detection error and shorter response time.