A rare regional severe convection process of Guangxi occurred in 24-25 January 2020, which was accompanied by the maximal range hail process since 2000. The abnormal development and eastward of the southern branch trough (SBT) were the disturbance backgrounds that provided necessary thermal, dynamic and water vapor conditions. Based on conventional observation data, FY-2G satellite data, NCEP/NCAR and ERA5 reanalysis data, the SBT inducing the regional severe convection process is analyzed from the perspective of energy conversion. The results show that the mid-latitude and subtropical westerly jets were stronger than those in the same peried in history during the whole process, which were conducive to the upstream disturbance spreading. There were two active Rossby wave trains over the northern and southern Eurasia respectively. The southern subtropical westerly jet Rossby wave originated from the Mediterranean Sea played a major role in regulating the SBT. The Rossby wave energy dispersed along the jet stream and converged in SBT region, promoting the development and eastward of SBT. The northern one originated from the North Atlantic blocking played a synergistic role, promoting the development of the Urals cold trough and its merger with the Middle East trough, thereby enhancing the propagation of the southern one and further enhancing the SBT. The conversion from synoptic-scale available potential energy and the transport of kinetic energy from background field to synoptic-scale were the main contributions of synoptic-scale disturbance of SBT. The advection transport of kinetic energy redistributed the obtained synoptic-scale kinetic energy in space and thus maintained the stable development of SBT and moving eastward. Under the above background, the downscaled kinetic energy cascade from synoptic-scale to convective scale became the main energy source of regional severe convective, and the stable conversion of convective scale available potential energy to kinetic energy promoted the occurrence and development of the convective disturbances in the middle and low troposphere.