In order to reduce the interference of ambient temperature changes to the single defect photonic crystal sensing, a double defect mode sensing model of air gate photonic crystal is proposed. The mechanism of the double defect mode is analyzed by tight- binding method, and the optical transmission property of the photonic crystal structure is analyzed by the transmission matrix method. For the cross- sensitive issue of temperature and refractive index, a method to eliminate the temperature interference is proposed, and the relation model between the two defect mode wavelengths and the structure parameters of the photonic crystal are established. Using the air gate photonic crystal structure, the dynamic monitoring of the detected gas sample parameters can be achieved from the shift of the resonant transmission peak. The numerical simulation shows that the relation between double defect sensor has the features of double defect mode wavelengths and the gas refractive index is linear. The sensor has the advantages of simple structure and high precision.