Abstract: The Northeast Cold Vortex (NECV) rainstorm that occurred in Liaoning and Jilin provinces during June 2–3, 2021, was explored using multisource observation and reanalysis data and high-resolution numerical simulations of the main precipitation period produced by the Weather Research and Forecasting Model (WRF), combined with three-dimensional precipitation diagnostic equations, to perform a comprehensive study on the macro- and microphysical processes and the rainfall mechanism. It was revealed that the precipitation was widespread, with strong local rainfall and prominent convection. During the rainstorm, the East Asian atmospheric circulation was relatively stable, and the NECV moved slowly eastward, carrying cold air southward and converging with southerly warm-wet airflow, consequently developing a vortex cloud system. Liaoning and Jilin were located to the left outlet of the high-level jet and to the front of the low-level jet, and the dynamical structure of high-level dispersion and low-level convergence contributed to precipitation development. The intensification of vapor convergence was accompanied by vigorous development of cloud physical processes and a significant increase in water species, with graupel mainly contributing to precipitation through cloud physical processes such as melting into raindrops. Cloud droplets grew rapidly via vapor condensation and were consumed largely during cloud microphysical transformations for cloud system development and precipitation. Precipitation intensity was affected by both vapor and cloud budgets. In the early precipitation stage, along with a significant increase in vapor transport and convergence, the local vapor content increased, and precipitation systems developed. Then, the local convergence weakened as the cold vortex cloud system gradually moved eastward, and the local vapor depletion continued to support heavy precipitation. Exuberant development of water species (especially the ice phase) accompanied local vapor convergence. In the early stage, the rapid development of precipitation clouds was supported by a combination of liquid-phase hydrometeor convergence and microphysical transformation processes. These processes remained active at the peak of precipitation; however, local changes in hydrometeors were not evident because of the depletion of heavy precipitation. The liquid hydrometeors continued to converge throughout the storm, while the ice ones gradually exhibited weak divergence after a short period of convergence at the start. This evolutionary feature was associated with local thermal and dynamical structures and their evolution.