Low-carbon transition is one of the key issues in the global energy sector today. The Guangxi Zhuang Autonomous Region, as a large electricity consumption and production area, also faces an urgent need for low-carbon transition. This paper aims to explore the low-carbon transition of the Guangxi power system, with a particular focus on the supportive role of hydropower and pumped storage in the process. Aiming at minimizing operational costs, we constructed a regional power system optimization model considering constraints such as unit output efficiency, startup costs, reservoir capacity, and the operational characteristics of various units. Subsequently, we proposed a comprehensive benefit evaluation index system that includes key indicators such as installed capacity, peak-shaving capability, carbon emissions, and system costs. Then, the basic characteristics of the Guangxi power system in 2025, 2030, and 2050, and the impact of hydropower and pumped storage on the low-carbon transition were investigated. The results indicate that the model and evaluation system proposed in this study can effectively support energy transition from both technical and economic perspectives. Properly configuring pumped storage capacity plays a crucial role in balancing the load and supply of the power system, as well as in enhancing system stability and reliability. This in-depth study provides valuable references for the development of the Guangxi power system, which is conducive to the promotion of sustainable energy and the establishment of a low-carbon power system.