Abstract: Certain critical lines in the power grid have serious impacts on large-scale blackouts, as well as the protection misoperation. In order to prevent the occurrence of the blackout accident effectively, an identification method of critical line in power grid is proposed by considering protection misoperation in this paper. In view of maximum network flow, an important degree index of node structure is put forward, which can fully reflect the structure characteristics of network connection, and overcome the defects that power flow flows in the shortest paths between buses in complex network model. In order to effectively reflect the actual situation of power grid, by considering protection misoperation, an index of protection vulnerability of branch lines is defined, which can effectively quantify the impact of protection failure on the critical line identification. Therefore, a comprehensive model for identifying critical lines is presented by combining structure vulnerability and protection vulnerability of branch lines. Taking IEEE 39-bus system as the testing example, the rationality and validity of the proposed model are verified by the example results.