To study the mesoscale characteristics and causes of extreme short-time heavy rainfall at night in Tianjin，by using encrypted automatic station data, min precipitation data, Doppler weather Radar data, wind profile data and the 5th generation global Atmospheric Reanalysis product (ERA5) of the European Center for Medium-Range Weather Forecasts, an extreme short-time heavy precipitation occurred in Tianjin in the early morning of July 3, 2022 was diagnosed and analyzed. The results show that: There was no significant low-value weather system at 500 hPa and no synoptic low-level jet background at the lower level. It was a rainstorm process mainly caused by small and medium scale forcing under atypical circulation situation, with obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused precipitation was presented in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echo organizations, and its radar echo had a high centroid, showing the characteristics of continental strong convective echo. The enhancement of the 975hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the ground, and synergizing with enhanced instability caused by mid-level dry cold air intrusion, which were the main reason for the triggering of the initial convection. The cold pool formed after precipitation formed a clear and irregular outflow boundary with the ambient wind, and the forcing action of the bottom cold pool led to the formation and development of γ-mesoscale vortex in front of the outflow boundary. The ageostrophic wind rotation caused by the inertial oscillation of the boundary layer at night and the gradually formed inversion stratification made the warm and moist air from the southeast from the sea continuously strengthen into the boundary layer jet, and then caused the vertical wind shear of 0-2.5km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhanced cold pool reached a temporary equilibrium. Resultly, the vortex in front of the outflow boundary continue to strengthened and developed from the bottom to up, and the strong dynamic convergence accompanying the vortex directly leaded to the rapid growth of minute-level rain intensity and lasted for several minutes, which finally leaded to the emergence of extreme short-term heavy precipitation. The results provide a reference basis for predicting local short-time heavy precipitation at night and exploring its occurrence and development mechanism in North China.