Using the reanalysis data of European Centre for Medium-Range Weather Forecasts (ECMWF) and the HYSPLIT model, the mean circulation background, main influence systems, physical quantity fields, and the 120-h backward trajectory characteristics of air parcel during 5 extreme precipitation processes in the Yuan River Basin are analyzed. The results are as follows. (1) When the extreme precipitation occurs, the Yuan River Basin is in the divergent airflow of the east side of the South Asia high at the upper level, controlled by the southwest airflow near the 584 dagpm isoline at the middle level due to the moderate position of the subtropical high, and located on the shear line at the lower level, with strong southwest airflow conveying energy and water vapor to the precipitation area. (2) In terms of physical quantity field, there are low-level convergence and high-level divergence near the Yuan River Basin, and the vertical velocity, water vapor distribution, and water vapor flux divergence fields are all conducive to the occurrence of rainstorm weather in this region. (3) Compared with the average t-lnp diagram of general rainstorm events in the Yuan River Basin, the extreme rainstorm has better energy conditions, stronger convective precipitation, and more abundant water vapor conditions. (4) In general, there are 5 water vapor trajectories for extreme precipitation in the Yuan River Basin. The southwest water vapor trajectories originated from the vicinity of the Bay of Bengal, the south of Indochina Peninsula, and the south of Yunnan are the most, accounting for 59.5% of the total trajectories; while the second is the south water vapor trajectories originated from the South China Sea, mainly located below 1 500 m, accounting for 15.0% of the total trajectories.