The ramose electrical dissection relationships and bidirectional electrical dissecting algorithm are presented to solve various electrical dissecting problems. They can be effectively used to acquire electrical supply and demand for power sources and power flow paths in a power network. This approach is based on analyzing the existing united electrical dissection relationships between power source and power flow path in a power network to obtain the primary electrical dissecting parameters， and then based on the ramose electrical dissection relationships to obtain the full electrical dissecting parameters. Example and verification results prove the correctness of the proposed bidirectional electrical dissecting method.