Making full use of existing equipment under the new conditions, and trying to reduce the cost, this paper proposes the isolation and control strategy for smart substation MMS, GOOSE, SV three-in-one communication network overload fatal fault. Combined with the use of the simplified topology, dynamic layer two protocol (IEC62439, PrivateLoop, LoopDetection, STP/RSTP/MSTP, GMRP, IGMPSnooping), static configuration (VLAN, multicast, layer three routing, policy routing, ACL), overload monitoring and overload control, the reliability of network is improved. The combined VLAN, layer three switching, policy routing isolated topology, policy routing support core switch load balance is analyzed, the communication design and configuration of measuring and protective device are simplified. The communication equipment innovation overload monitoring and blocking solution is developed, which changes the traditional single means of suppression. The problems and advantages of dynamic and static configuration in three in one network are analyzed, and according to the levels and reliability requirements of smart substation, the different isolation strategies are selected. If the overload is monitored by communication equipment, first overload self recovery treatment is made, and by using hard wiring alarm and local log, the alarm information is sent to the monitoring host via MMS network simutaneously. If self recovery is failed, overload isolation is adopted to try to reduce the influence range of overload, waitting for the timely treatment of administrator.