Abstract: Based on multiscale diagnosis method of energy budget, the missing-forecast coastal warm-sector rainstorm process of Guangxi occurred in 24-26 January 2020 was analyzed by using the stational data, Doppler radar, FY-2G satellite data and the ERA5 reanalysis data. The results are shown below: The warm and moisture southwest jet in front of the southern branch trough provides a favorable synoptic condition for the rainstorm. The convection system was constantly triggered by the trumpet topography in the northeast of Vietnam, and moved northeastward to the coastal of Guangxi, which was influenced by the upper level airflow and produced significant amount of precipitation. It is found that the occurrence and development of warm-sector rainstorm were mainly dominated by the convection-scale kinetic energy that correlated well with the former in evolution. The convective energy mainly come from the middle and lower troposphere and losts in the upper troposphere. The kinetic energy from the background scale contributed the most, and the barotropic instability of the background flow field in the middle and lower troposphere dominated the development of rainstorm in the warm-sector. The buoyancy conversion of convection-scale available potential energy to kinetic energy in the middle troposphere further promoted the development of system. The transport of kinetic energy made the convection-scale kinetic energy distribute evenly spatially, which led to the stable development of the convective system and enabled it to maintain for long time and thus produce large amount of precipitation over its path. The contribution of synoptic-scale kinetic energy conversion and pressure gradient work is small, which reflects the nature of weak synoptic-scale forcing of warm-sector rainstorm.