An. open. and. thncfionally. distributed. Energy Management System(EMS)is described in this paper The advanced application software of the EMS is coded with C language and run RISC workstation with UNIX operating system. This EMS is a completdy open one and can be installed on any existing SCADA to upgrade the SCADA t0 EMS. Almost all the network analysis,functions have been implemented in the EMS.It has been put into on-line operation in Henau Power System(HNPS)control center in China Tbc hardware configuration and software design are described Majn funcfiorts of the EMS are described The core techniques and. agmithms adopted in the EMS are introduced. The on-line operation experiences of the EMS in HNPS are also reported The distinquished advantages ofthe open and functionally distributed EMS over the conventional centralized ones are verified.