The single step power flow calculation of PSS/E based on man-machine interface have problems such as heavy workload in model maintenance and poor scalability. An extensible PSS/E power flow calculation method based on CIM/E full model is proposed. By using hierarchical network model database as interlayer, CIM/E model is parsed into the interlayer database and the synchronized PSS/E calculation database is generated simultaneously, and full physical model of power grid is built automatically. Interface layer is built based on API secondary development and packaging, and power flow calculation is run automatically and periodically by flow control of PSS/E through external application. By using hierarchical network model database as input and output interface to receive and process device operational order from external application, interaction of device operation is realized automatically. Based on real-time topological analysis of hierarchical database, the topological problems of PSS/E simulation with full model are fixed, which ensures the validity of topological analysis. East China Power Grid model is used for practical application, and the simulation results verify the validity and practicality of this method.