When the spaceborne ultraviolet hyperspectral atmospheric composition spectrometer is in orbit, it obtains radiation and spectral information through the light path of the earth light observation as well as the light path of the sunlight observation, so it is necessary to be calibrated in the laboratory before launching. As the irradiance calibration coefficient will be used for obtaining the solar reference spectrum during the on-orbit observation, the calibration accuracy directly affects the instrument′s on-orbit detection and inversion accuracy, and determines the reliability of remote sensing information. The direct diverging light is used in the irradiance calibration method, and a two-dimensional calibration platform is build to carry out a series of tests at different angles and distances on the calibration light path. By using the least squares method to linearly fit the experimental values at three distances, the irradiance calibration coefficient is obtained, and then the influence of the angle and the other factors is corrected. The calibration results show that the combined uncertainty is 3.42%, which meets the requirements of radiation calibration, indicating the feasibility ofthe method.