Abstract: In view of problems of large nonlinear error and low accuracy of approximate linear output curve of carrier catalytic gas sensor, the paper proposed a method of using the least square method to establish function relationship between output voltage and gas volume fraction of carrier catalytic gas sensor. It took MJC4/2.9J carrier catalytic element as experimental object, combined with corresponding experimental data to get fitting curve of output voltage and gas volume fraction, the fitting curve result showed that the function relationship between output voltage and gas volume fraction of gas sensor by using the least square method has small nonlinear error and high accuracy. The function relationship was applied to design of gas detector, the actual application result showed that the gas detector has higher accuracy and stability.