The invention discloses a method and system for optimizing power system simulation data based on the XML. The method comprises the steps that a simulation terminal based on transformer substation simulation carries out a registration service on a server based on power grid simulation, and needed service data are purchased from the server based on power grid simulation; the server based on power grid simulation sends the needed service data to the simulation terminal based on transformer substation simulation according to the purchasing requirement based on the XML data format; after receiving the XML data format, the simulation terminal based on transformer substation simulation obtains the service data in the XML data format in an analysis mode and the operation interface related to the simulation terminal is refreshed. According to the method and system for optimizing the power system simulation data based on the XML, optimized XML data files are transmitted according to a purchasing method, only the modified data are transmitted in the data exchange process, void transmission of data is reduced, and high-efficiency application of a transformer substation simulation platform is improved.