Abstract: Based on the tropical cyclone best track data from Shanghai Typhoon Institute of China Meteorological Administration and the geostationary infrared satellite cloud image from April to November during 1979-2019, 189 typhoons formed in the South China Sea are selected as target cases. The circulation characteristics, dynamic and thermal conditions from 48 hours before typhoon formation to the time of typhoon generation are analyzed using the reanalysis data of the European Centre for Medium-Range Weather Forecasts (ECMWF) with 1°×1° grid. The results indicate that the typhoon in the South China Sea is formed in a large range of tropical ocean with high surface temperature, high water vapor content and unstable stratification. The development of deep convection and its distance to the tropical disturbance center can be used as an observation criterion for whether the tropical disturbance can develop into typhoon in the next 48 hours. Intertropical convergence is the dominant background circulation of typhoon formation in the South China Sea, and south-west monsoon or easterly wave are also main large-scale circulation. The center of typhoon disturbance is often in the transition zone of the vertical shear, where the vertical shear of the north side of the disturbance becomes smaller and the vertical shear of the south side becomes larger. Sometimes the disturbance center is slightly inclined to the weak vertical shear center. As a whole, there is no significant correlation between wind vertical shear and typhoon disturbance development. The center of tropical disturbance generally coincides with the center of vertical vorticity, and the center of vertical vorticity could be considered as a physical quantity representing the strength of disturbance itself. Furthermore, it is difficult to define the development of the vertical vorticity as an indicator to characterize the development trend of disturbance, while the Okubo-Weiss (OW) index is a good indicator for the development of disturbance and the determination of the disturbance location. In the process of typhoon disturbance development, there is a potential vortex column running through the whole troposphere near the disturbance center. Within the potential vortex column near the disturbance center, the interaction between lower disturbance and the potential vortex in middle and low layer is beneficial to the development of typhoon disturbance.