Timely and effective identification of vulnerable links in power grid is important to prevent the occurrence of large-scale blackouts. To achieve this process, an identification method based on the real-time fault model of protection was proposed. A probability model of protection fault was established according to historical protection system statistics and continuous time discrete state Markov process ,and based upon all, quantifying the real-time probability of failure to operate and undesired trip of protection reasonably by considering real-time operating conditions of power grid. The protection fault events was established by simulating the protection fault and operation mode according to the spread characteristic of failures,and defining the protection fault vulnerability by applying risk theory to combine the probability of protection fault and the consequences of fault,weighing the impact of protection fault on the grid vulnerability,thus the system vulnerable links can be identified. The results of simulation demonstrate the effectiveness and rationality of the method.