The invention relates to an energy management system, comprising a data acquisition layer, a monitoring analysis layer, a diagnosis optimization layer, an energy saving synergy layer, and an integrated reporting layer. The data acquisition layer is used for collecting user energy consumption data; the monitoring analysis layer is used for analyzing the user energy consumption data and obtaining abnormal user energy consumption data; the diagnosis optimization layer is used for making an optimization scheme according to the abnormal user energy consumption data; the energy saving synergy layer is used for executing the optimization scheme, and obtaining the optimization result of the abnormal user energy consumption data; and the integrated reporting layer is used for managing a user energy consumption data report after management optimization, and returning optimized user energy consumption data to the monitoring analysis layer. The energy management system utilizes the PDCA circulating theory in the management science and combines with a management and technical means compatibility concept to establish energy management system functions, and aims at improving energy management efficiency gradually in a spiral rising mode in practical application.