Abstract: Based on the surface observation data, typhoon track data, TBB of Satellite FY-2G and the reanalysis data of NCEP, the causes of a rainstorm which was happened in the high altitude mountainous area of western Panxi Area in July 2019 is analyzed by synoptic diagnosis. The results indicate that in the rainstorm process, the Tropical Storm Mun formed by the development of the South China Sea monsoon depression and the low-level peripheral airflow of the Indian monsoon low intersect in the western part of Panxi area and form an obvious convergence. At the same time, the topography has a forced lifting effect on the low-level warm and humid airflow, the position and intensity of low-level mesoscale convergence line have a good corresponding relationship with mesoscale convective clouds. The obvious water vapor convergence in the lower layer, the stong upward movemnet in the middle layer and the maintenance of unstable energy in the lower layer are conducive to the generation of rainstorm.