The invention relates to a system for optimizing a unit maintenance plan by considering the adjustment capacity of a large-scale ultra-high-voltage power supply. The system comprises a database module, an input module, a maintenance plan optimization module and an output module, wherein the database module is used for storing unit data, load data, ultra-high-voltage data and maintenance data; the input module is connected with the database module and used for transferring data in the database module; the maintenance plan optimization module is connected with the input module and used for performing optimization calculation of the maintenance plan according to the data obtained by the input module and obtaining an optimal maintenance plan arrangement; and the output module is connected with the maintenance plan optimization module and used for inputting the optimal maintenance plan arrangement and a corresponding week risk degree average value. Compared with the prior art, the system disclosed by the invention is high-efficiency and practical; maintenance plan arrangements of all units including the large-scale ultra-high-voltage power supply can be considered; and the systematic risk degree is optimized in a unified manner in the perspective of a power supply side whole.