Because of radar beam occluded seriously by terrain, the quality of echo data is greatly disturbed. In this paper, the DEM (Digital Elevation Model) data of SRTM (Shuttle Radar Topography Mission) task and Google Company are used to calculate the beam occlusion rate of Sband radar at low elevation angle at Nanjiao of Beijing, and the echo reflectance correction relationship for the partial occlusion area is established. In the process of a largescale stratiform precipitation in Beijing on 19 May 2018, the qualitative and quantitative comparative analysis of the radar quantitative estimation of rainfall before and after the beam occlusion correction and the observation results from three rain gauges on the ground are performed. The results show: (1) Beam occlusion correction helps improve the spatial continuity of the reflectivity factor. The reflectance difference between 0.5° and 1.5° of elevation angle after the beam occlusion correction is reduced as a whole, which is consistent with the vertical profile of the stratiform cloud precipitation. (2) On the same day, between 09:00 and 11:00, the accuracy of the radar Quantitative Precipitation Estimation (QPE) after beam correction is improved. Using the Grading Standard Error and the Normalized Mean Bias (NMB) to evaluate the error between QPEs before and after the beam occlusion correction and measured values from the rain gauge, the result shows that the reflectivity after beam correction is more consistent with the measured rainfall from the rain gauge.