Abstract: The integration of the large-scale wind farm and the growing amount of the electric vehicles deteriorate the unbalanced urban load distribution, which increases the operation risk, especially during the peak load time. In order to enlarge the transmission security margin, the operators usually resort to switching the main and reserve lines in high voltage distribution network (HVDN) to transfer the loads. Besides, the uncertainty output of the wind farm also expands or shrinks the security margin. In an attempt to assess this resilient security margin appropriately, a probabilistic evaluation model based on the three-point estimate method and Cornish-Fisher expansion were established. In addition, the Resilient Steady State Distance (RSSD) index was defined to describe the current Resilient Security Margin (RSM). And the influence of the flexible HVDN topological structure was also detailed in the paper. Simulation results showed that the proposed evaluation model can achieve the resilient probabilistic evaluation of the urban transmission network security margin and provide reliable indicators for operational decision making.