Abstract: The emergency power supply system of a nuclear power plant is a critical safety barrier for achieving safe reactor shutdown, removing residual heat, and preventing the release of radioactive substances under accident conditions. It must provide reliable and continuous power supply to safety-related equipment during both design-basis accidents and beyond-design-basis accidents, and support the continuous implementation of accident mitigation measures. This study takes the VVER unit of Tianwan Nuclear Power Plant as the research object, and systematically analyzes the overall architecture, key equipment characteristics, and operational logical connections of its low-voltage emergency power supply system. Adhering to the design principles of redundancy, independence, and diversity, the system consists of battery and inverter systems, AC uninterruptible power supply systems, as well as corresponding power distribution and control equipment. Each series is physically isolated to effectively avoid common-mode failures. The research elaborates in detail on the system's operating modes and switching mechanisms under normal operation, emergency operation, and design-basis accidents such as station blackout. Based on long-term operational data, it identifies weak links including equipment aging, redundant configuration, and maintenance strategies. Combining the plant's actual operational needs and safety objectives, the study proposes system optimization and improvement strategies to comprehensively enhance system reliability and emergency response capabilities, thereby providing references for the safe and stable operation of similar VVER units.