Abstract: Solar irradiance spectroradiometer was a new type of instrument for solar direct continuous spectrum irradiance measurement. To meet the requirements of the high-precision observation, a system-level calibration method based on tunable laser was developed. In this method, the uniform irradiance source was acquired from the tunable laser-illuminated integrating sphere, and the standard irradiance detector was used as transferring standard, so the spectral irradiance responsibility of solar irradiance spectroradiometer can be traced to the cryogenic absolute radiometer. The experiment of the 870 nm channel was carried out. The deviations with the standard lamp and Langley are 2.84% and 4.08%, which validates the rationality of this method. According to the evaluation of uncertainty specification, the uncertainty of this method is 0.882%, which can improve the measurement of the solar spectral radiation.