A method for detecting the high-pressure sealing performance of a gas system after an impact test of a compressed natural gas vehicle, including installing a high-pressure sensor with a characteristic curve on an air inlet pipe of a pressure reducer, and inflating a high-pressure pipeline with compressed gas under a safe pressure; inflating the gas system with compressed gas to a normal working pressure before the impact test of the compressed natural gas vehicle; collecting a voltage value by the high-pressure sensor within 1-3 hours, and determining that the sealing performance of the gas system of the compressed natural gas vehicle is satisfactory when a detected voltage drop value is smaller than a preset value; otherwise, determining that the sealing performance of the gas system of the compressed natural gas vehicle is unsatisfactory.