When the gas concentration to be measured is high, the absorption loss in the cavity is large, which limits the measurement range of cavity ring-down spectroscopy. To solve this problem, the correlation between sampling threshold and gas concentration detection is analyzed, the influence of threshold adjustment on measurement accuracy is simulated, a model describing the dynamic response ranges of threshold and gas concentration is established, and a method for detection range extension is proposed by adjusting threshold. In the experiment, the methane standard gases with different concentrations are measured by the measurement device based on cavity ring-down spectroscopy, and the measured results are consistent with the theoretical simulation results. By adjusting the measurement threshold, the range is extended to 1×10 -4 (volume fraction), the dynamic response range is 2.72×10 4, and the maximum quoted error is 0.78%. The proposed method solves the problem that low detection limit and large range cannot be met simultaneously in the technology based on cavity ring-down spectroscopy and provides an analytical method for the setting of threshold parameters.