Abstract: Based on the conventional high-altitude observation data, ground densified observation data and ERA5 reanalysis data (0.25°× 0.25°), the cause diagnosis and predictability of the continuous rainstorm process in Shaanxi from August 4 to 7, 2020 were analysed. The results show that the rainstorm process can be divided into two stages, namely, the rainstorm in northern Shaanxi on August 5 and the rainstorm in central and southern Shaanxi on August 7, the circulation background of the two rainstorms was significantly different. The main synoptic systems affecting the rainstorm on August 5 were upper trough, low level jet and low vortex. The middle and low level jet was strong and maintained for a long time, the vorticity was large, the convergence was strong, the positive vorticity advection was significant, and the synoptic scale forcing was strong. The main synoptic systems affecting the rainstorm on August 7 were short-wave trough and low-level shear, the wind speed in the middle and lower atmosphere was weak, the vorticity of the system was small, the convergence was weak, and the synoptic scale forcing was weak. From August 4 to 5, the water vapor transport in the middle and lower atmosphere was strong, and the water vapor transport was 3~4 σ larger than the climatic state. The southwest jet stream at 700 hPa and southeast jet stream at 850 hPa brought abundant water vapor supply to northern Shaanxi. There was an obvious vortex in the middle and lower atmosphere, and the vorticity center was 4~5 σ stronger than the climatic state in the eastern part of Northern Shaanxi, at the same time, there was an obvious frontogenesis on the south side of the vortex, and the secondary circulation strengthened the updraft, the water vapor strongly converged and lifted in the center and right side of the vortex, and the rainstorm was maintained. The conditional symmetric instability existed between 800 and 700 hPa, which further enhanced the upward motion, the main reason for the extreme rainstorm in northern Shaanxi was the abnormally abundant water vapor supply and continuous upward movement caused by the abnormally strong low vortex. From August 6 to 7, the water vapor transport in central and southern Shaanxi was weak, and the intensity of water vapor convergence was small, but the local precipitable water was large. The rainstorm area was controlled by warm and wet atmosphere, with strong convective instability and large convective available potential energy, the convergence and uplift of shear line triggered the development of convection, the convective nature of precipitation was more obvious, the heavy precipitation was more dispersed, the rain was strong and the duration was short, which was closely related to the terrain.