To investigate the characteristics and causes of the extremely severe precipitation process in Northwest Yunnan from June 28 to July 1, 2024, we conducted a synoptic diagnostic analysis of the severed precipitation process by using ERA5 reanalysis data and daily precipitation data from 109 meteorological stations in Nujiang Prefecture of Yunnan Province. The results indicate that: (1) The convergence zone of cold air and warm, moist southwestern airflow gradually shifted southward with the convergence of strong winds at 700 hPa, leading the severe precipitation to develop from north to south. (2) During the period of severe precipitation, the middle and lower troposphere were characterized by high moisture content. The orographic blocking effect facilitated the transport of low-level water vapor to the middle and upper levels, resulting in strong moisture convergence in the west side of the Nujiang River, thus providing abundant water vapor. (3) The severe precipitation area had divergence in the upper troposphere and convergence in the lower troposphere, situated within an environment of high energy and high humidity. The northern part of Nujiang was dominated by strong warm advection, which was conducive to upward motion. The intrusion of cold advection in the middle to upper levels over the southern part of Nujiang caused unsaturated air to get to saturated, reducing the stability of the atmospheric stratification and providing favorable conditions for the release of energy and latent heat. Combined with the orographic forced uplift, the vertical upward motion was further strengthened. (4) The convergence of dry cold air and warm moist airflow led to a rapid intensification of disturbances, promoting the development of precipitation. During the severe precipitation event, the isentropic potential vorticity (IPV) value in Nujiang exceeded 0.5 PVU, and even up to 0.8 PVU in some isolated areas, which indicates that there existed a significant correlation between the occurrence of severe precipitation and the development of IPV disturbances. Therefore, in the complex topography of the Northwest Yunnan, it is essential to fully consider the influence of terrain in the forecasting operation to make the forecast more accurate.