According to the architecture of a unified substation communication network， a dynamic simulation model of the IEC 61850 based digital substation communication network is developed using the electric power and communication synchronizing simulator（EPOCHS）. According to the network simulation requirements， the linkage among physical subnets is established in network simulator（NS2）， and the virtual local area network（VLAN） multicast and message transmission prioritizing mechanism is implemented. The transmission of sampled value（SAV） message and generic object oriented substation event（GOOSE） message are simulated and the real-time performance is analyzed. The result can be used as a reference for selection of network bandwidth， partition of VLAN and priority setting of message transmission.