In order to better understand the mechanisms of rainstorms in South China and to improve the accuracy of rainstorm forecasts, this article reviews the major research advances over the past decade on the impact of mesoscale and small_scale terrain on rainstorm water vapor, dynamics, thermal conditions, and cloud microphysical processes. The results are as follows: (1) Different scales of terrain significantly affect the position and intensity of the rain belt by changing the water vapor flux convergence and vertical transport. (2) The synergistic effect of dynamic terrain uplift and the continuous convergence of warm and moist air currents serves as the core mechanism. Local terrain can change the low_level flow field structure, trigger and organize the evolution of microscale and small_scale systems, and lead to rainstorms. Terrain_induced circum_flow can adjust horizontal convergence, reinforcing the intensification of rainstorms in conjunction with uphill airflow. (3) Topography can enhance the release of unstable energy, optimize convective triggering conditions, drive secondary circulation through local thermal differences, and rebuild the thermodynamic structure of heavy rainfall. (4) Terrain convergence enhances vertical motion, promoting the collision and growth of water condensation particles and their transport to the middle layer. The latent heat released by the melting and sublimation of ice particles forms a positive feedback loop, amplifying the intensity of rainstorms. Therefore, the influence of mesoscale and small_scale topography in South China on rainstorms is a multi_dimensional collaborative process. Its scale dependence and mechanism synergies need to be considered in rainstorm forecasting.