Competitive environment under progress of deregulation has been significantly changing the grid operational circumstances in Japanese electric power companies. The competitive environment requires extreme cost reduction of grid operation, which has been accomplished by the consolidation of separate control centers to reduce the number of control centers through reforming grid operational structure. Even in that reform, the back-up system of control center is essential to maintain reliability in case of natural disaster. Meanwhile improvement of computer performance and network performance comes to realize wide area IP-based EMS/SCADA system. This system is not only flexible on the consolidation and reform of grid operational structure but also suitable for highly reliable system operation even in case of large natural disaster. This paper presents the overview of wide area IP-based EMS/SCADAsystem and how it realizes flexibility and high reliability of system operation.