The invention relates to a high-voltage power grid theoretical line loss evaluation system which comprises a power grid pattern module, a line loss theoretical calculation module and a statistical analysis summarizing module. The power grid pattern module comprises a power grid wiring graph in-station graph drawing module, an electric element attribute data editing module, a pattern display and control module, a power grid pattern inquiring/editing/modifying module and a trend calculation result marking module. The line loss theoretical calculation module comprises a line loss theoretical calculation model module, a calculation result checking and correcting module, a grid loss calculating and reactive voltage optimizing module, and a line switching and transformer switching optimization calculating module. The statistical analysis summarizing module comprises a multifunctional multi-stage summarizing module, a sub-voltage grade calculating element analyzing and statistics module, a line loss reporting and line loss analyzing module, a data inquiring module and a data exporting module. The high-voltage power grid theoretical line loss evaluation system has functions of integrating and developing high-voltage power grid line loss calculation analysis summary, and furthermore summarizing high-voltage power grid line loss theoretical calculation results.