In this paper, a symmetrical all-dielectric metasurface structure is designed to achieve a high-sensitivity dual-parameter sensor. After coating a gas-sensitive thin film on the metasurface, two Fano resonance peaks labeled as dip 1 and dip 2 are generated to measure the refractive index and gas volume fraction simultaneously. The calculation results show that the refractive index and gas volume fraction sensitivity of dip 1 are 1035 nm/RIU and -0.57 nm/%, respectively, and the refractive index sensitivity and gas volume fraction sensitivity of dip 2 are 543.6 nm/RIU and -0.87 nm/%, respectively. The sensor can be used for high-sensitivity measurement of two parameters, and the transmission spectrum obtained using the symmetrical structure is not affected by the polarization angle of the light source, improving the adaptability of the sensor to the light source, and it provides a new method for detecting the environment.