To improve the efficiency of high temperature calibration in the visible light band (0.3 μm~0.9 μm), a simplified method for high-temperature calibration is proposed. Firstly, a high-temperature calibration model in the visible light band with exposure time variable is proposed. Based on a large number of experimental data, it is found that the gray value of each channel of an RGB camera varies linearly not only with the increase of exposure time, but also with the increase of black-body radiation brightness. Thus, a specific form of high-temperature calibration model in the visible light band is determined. To solve the unknowns in the simplified high-temperature calibration model in the visible light band, image data at two different exposure times are collected under two levels of black-body radiation brightness, and then the image data is processed to obtain the high-temperature calibration curve of the RGB camera under any exposure time. Finally, the simplified visible light band high-temperature calibration method proposed in this article is compared to the conventional visible light band high-temperature calibration method based on exposure time. The experimental results show that the maximum relative error between the calculated value of the R channel, G channel, B channel and the calibrated values are 3.38%, 2.56%, -1.14%. Moreover, the relative error between the calculated and the calibrated values for each channel does not exceed 3.50%. The mathematical model proposed in this article can effectively simplify the conventional high-temperature calibration method, resulting in a reduced high-temperature calibration time and improving the calibration efficiency.