The comprehensive observational analysis of the Northeast cold vortex (NECV) rainstorm that occurred in Liaoning and Jilin provinces on June 2-3, 2021 was?investigated?using multi-source observations and reanalysis data, and then a high-resolution numerical simulation of main precipitation period produced by the WRF, combined with three dimensional precipitation diagnostic equations, to carry out a diagnostic study of the macro and micro physical processes and the mechanism of rainfall. The results show that the precipitation was widespread, with strong local rainfall and prominent convection. During the rainstorm, the East-Asian atmospheric circulation was relatively stable, the NECV moved slowly eastward, carrying cold air southward and converging with southerly warm-wet airflow, which in turn triggered the development of a vortex cloud system. The two provinces were located to the left outlet of the high-level jet and to the front of the low-level jet, the dynamical structure of high-level dispersion and low-level convergence contributed to the development of precipitation. The intensification of vapour convergence was accompanied by the vigorous development of cloud physical processes and a significant increase in water species, of which graupel made an important contribution to precipitation through cloud physical processes such as melting into raindrops. Cloud droplets grew rapidly through vapour condensation and were consumed largely during cloud microphysical transformations for cloud system development and precipitation. Precipitation intensity was influenced by a combination of vapour and cloud budget. In the early stage of precipitation, along with a significant increase in vapour transport and convergence, the local vapour content increased and precipitation systems developed. Later, the local convergence weakened as the cold vortex cloud system gradually moved eastwards, the local vapour depletion continued to support heavy precipitation; Exuberant development of water species (especially ice-phase) accompanied local vapour convergence. In early stage, the rapid development of precipitation clouds were supported by a combination of liquid-phase hydrometeors convergence and microphysical transformation processes. The above two processes remained active at the peak of the precipitation, but local change of hydrometeors was not obvious due to the depletion of heavy precipitation. The liquid hydrometeors continued to converge throughout the storm, while the ice hydrometeors gradually turned into weak divergence after a short period of convergence at beginning, this evolutionary feature was related to local thermal and dynamical structure and their evolution.