Abstract: In order to improve the water vapor initial field of numerical model and QPF (quantitative precipitation forecast) with the satellite data fusion, the numerical simulation and sensitivity experiment were made on a short-term severe precipitation process occurred in southeastern Shanxi Province at night of July 9, 2013. The results showed that: the northwest low vortex moving eastward with the upper-level trough guiding was the circulation background for this severe precipitation, and the short-term severe precipitation process was mainly affected by the low-level vortex accompanied by wind shear, while the meso- β scale convection cloud system which generated near the shear line was the direct system. Precipitation forecast for 24 hours, especially forecast of severe precipitation, could be improved significantly by cloud top data fusion. Further study indicated that: cloud top data fusion could contribute to obtaining the information of mesoscale systems and finding out the meso- β scale convection cloud cluster; with the cloud top data fusion, numerical model could better depict the mesoscale characteristic of real humidity field, significantly enhance the analysis of high humidity regions which had an important influence on the severe precipitation; numerical model could more effectively forecast the change and movement of precipitation for 3 hours, which would significantly improve the effect of rainstorm nowcasting.