The invention, which belongs to the technical field of the gas-steam combined circulating generating system, relates to a big-data-based remote energy efficiency diagnosis method for a gas-steam combined circulating generator set. According to the method, under the big background of continuous accelerated fusion of industrialization and informatization, original operation parameters, collected at field, of a gas generator set are integrated and analyzed by an internet-based group private network. The system is composed of a real-time database and a relation database, a configuration application server, and a web server; the databases are used for data storage and transmission; the configuration application server is used for data calculation, analysis and application; and the web server is used for information web issuing and remote access. The diagnosis method includes: data acquisition, data information integration and analysis, data determination, on-line set operating state monitoring, real-time and on-line performance index calculation, operating parameter statistic analysis, performance index statistics and data mining analysis, and set benchmarking management.