This study develops a new cloud scheme of Global/Regional Assimilation and Prediction System (GRAPES) at 50 km spatial resolution, considering the impact of the detrainment process of shallow convection and boundarylayer clouds on hydrometeors water contents and cloud fraction. The purpose of this research is to improve the lowlevel cloud prediction of GRAPES model, simulate and compare the results before and after the improvement. Besides the results are compared with observational data of the Clouds and the Earth’s Radiant Energy System (CERES) and Year of Tropical Convection (YOTC). The results show that considering the detrainment process of shallow convection and boundarylayer clouds mainly increases the cloud fraction and liquid hydrometeor contents of lowlevel cloud below 700 hPa. The improved results are closer to observation. Boundarylayer stratocumulus clouds mainly affect the clouds near the top of boundary layer and the influenced thickness is less than 200 hPa. The impact magnitude of shallow convection detrainment process is equivalent to the one of boundarylayer clouds, but the impact thickness is more widely in the former. Shallow convection process will have a certain impact on the low clouds from surface to the height of 700 hPa. Further research shows that due to the improvement of lowlevel cloud prediction, forecast of cloud radiative forcing at surface and top of atmosphere could also be improved, the increasement of lowlevel clouds would directly enhance cloud radiative forcing at surface.