Abstract: In order to solve the problem of heat flux identification of temperature-sensitive paints under the interference condition of high-temperature gas radiation luminescence, based on the gradient change of radiation light intensity of the coating, a heat flux identification method using the Levenberg-Marquardt optimization algorithm had been established, and experiments were carried out using the flat plate-wedge model in the high-enthalpy shock tunnel, with the total temperature of 2 816 K and 4 620 K, respectively. The results show that the high-temperature gas radiation has an important influence on the optical measurement method, and the gas radiation luminescence is further enhanced with the increase of the total temperature of the incoming flows. The amplitude of the light intensity gradient on the coating surface gradually decreases with time and tends to be stable. Under different total temperature conditions, in the flat area with a small temperature rise, the maximum value of the gas radiation light intensity gradient amplitude in the total gradient amplitude is 16.9%, accounting for less than 4.8% in areas with large temperature rise. The global optimal heat flux identification method based on gradient change can effectively eliminate the influence of high-temperature gas radiation, and the difference between the measurement results of temperature-sensitive paint and the thermocouple measurement results is less than 20% in the non-disturbing area of the plate and the peak heat flux area of the wedge.