Abstract: Using the comprehensive observation data of ground meteorological station, LMF1.0 three-dimensional lighting positioning monitoring, CMA Multisource Precipitation Analysis System(CMPAS) products, cloud-top brightness temperature from FY-4A and ERA5 reanalysis data, a mountainous torrential rain in Panxi region, the southeastern margin of Tibetan Plateau during 20-21 August, 2023 was analyzed comprehensively. The following results were obtained: (1) The mountainous torrential rain was effected by the shear lines which provided favorable dynamic conditions for the occurrence of Mesoscale Convective System (MCS) at 500 hPa and 700 hPa under the background of weak synoptic scale, and the backward development of MCS was more obvious. (2) The continuous convergence rising motion was conducive to the development and maintenance of strong convective precipitation under the condition of high energy, high wet and convective instability stratified in the lower and middle layers. The updraft of local meridional circulation aggravated the releasing of latent heat through condensation of water vapor in the torrential rain area, resulting in the occurrence of extreme short-term heavy rainfall. (3) The blocking effect of the large topography of the southeastern margin of the Tibetan Plateau on the easterly and southerly airflow of the Yunnan-Kweichow Plateau caused a large accumulation of water vapor in the lower and middle atmosphere of the Panxi region. The strong water vapor convergence in the boundary layer and the strong vertical water vapor flux in the middle and upper atmosphere played a key role in the occurrence and maintenance of local persistent heavy rainfall. Most of the water vapor transport in the heavy rainfall area was concentrated in the boundary layer to lower atmosphere, which was dominated by the eastward to southward path of the Yunnan-Kweichow Plateau. The evolution of net water vapor budget had a certain indicative effect on the development of precipitation.