A description is made of an online multi-regional model splicing and merging method based on the CIM/XML power system models and SVG graphs and with the tie lines as modeling boundaries for the power ensured automation system. In view of the teed tie lines between regional systems， tee grouping is presented to merge the tee connections from several models and prevent frequent modification of the line information due to non-unified naming of virtual substations. As for the incremental model update， apart from updating the attributes of devices on the basis of unified naming， the connection between equipments will be updated by binding the connectivity of the operating system to that of the model to be imported. By means of the model's online splicing and merging， the power ensured automation system developed will be capable of retrieving a power supply path for important customers from 380 V to all upper level power sources through the network topology. Thus the requirement of“the whole chain” network monitoring can be met， guaranteeing as much as possible reliable power supply to important customers.