Abstract: In view of problems that infrared gas sensor is easy to be interfered by external optical source and electromagnetism, and its output signal is mixed with a lot of noise to affect detection precision, signal conditioning and data processing circuit of infrared gas sensor was designed. The circuit combines hardware with software. Signal conditioning circuit was designed in hardware, which has the extremely good enlargement filter function during meanwhile guarantees the signal authenticity. Way of median average filtering algorithm was used to process signal in software, which can effectively overcomes noise mixed in the signal and has good inhibitory action to the interference produced periodicity or thermal noise. The experimental results show that the circuit can filter out a lot of noise of sensor effectively and extract useful signal accurately of signal, improve detection accuracy and stability of sensor and its full scale measurement precision may reach 0.54%.