In order to satisfy the dynamic variation of power system configuration， the equivalent impedance calculation of the bus has to consider the outage of one or more branches from the bus to the system. It is essential for the terminal buses to determine the corresponding switching buses near the power system through topology analysis. Based on an analysis of the electro-physical topology paths described by the parameters in the equivalent network， a new algorithm of network topology analysis for equivalent impedance calculation is presented. By combining the physical topology and geometrical topology， the algorithm proposed has excluded the ineffective directions of geometrical path search through the judgment of electro-physical paths， thus ensuring that the search is directed to the power system from beginning to end and the complex back-tracing and depth searching of radial branches avoided. The research and examples show that the algorithm presented is simple and effective in accurately judging the terminal buses and determining their corresponding switching buses.