Abstract: With the continuous integration of power grid and information network, the vulnerability analysis of power cyber physical system considering the interaction between two networks has important practical value to ensure the stable operation of power system. In this paper, based on the complex network theory, a topological model of power cyber physical system is established, and an entropy index of topological structure of power cyber physical system is proposed, which takes into account the differences of nodes, edge differences and node dependencies. This index can overcome the limitation of the entropy index of single-layer network structure and identify the influence of important nodes in the power cyber physical system on the vulnerability. Taking a provincial power cyber physical system as an example, the simulation results show that the dependent network is more fragile than the single network, and nodes with high betweenness and high degree play a key role in maintaining the operation of the system, and if a few nodes with low degree and low betweenness fail, the robustness of the system will be reduced.