In order to realize long-term automatic observation of surface reflectivity and improve the frequency of site calibration, a method of surface reflectivity measurement based on ratiometric radiation measurement is proposed. Synchronous observation is carried out by using spectally-reflective automatic spectroradiometer and hyperspectral irradiance meter. Surface radiance and total atmospheric illuminance at the same time are obtained, and the surface reflectance parameters can be obtained by the ratio method. The laboratory radiation calibration based on standard radiation source is designed to obtain the calibration coefficients of the radiometer and illuminometer respectively, and then the input system parameters based on the ratio method to measure the surface reflectivity are obtained. The standard board measurement comparison experiment is carried out outdoors. The relative deviation between the visible-near-infrared ratio radiation measurement and the reference plate reflectance value after laboratory calibration is within 3%, and the effectiveness of the measurement system is verified.