Abstract: The active distribution network is a new distribution network form formed after connecting new energy sources such as photovoltaic and energy storage. In power system, load margin is an important index to measure voltage stability. It is difficult to accurately analyze the multi feeder network due to the expansion of the power grid scale and the increase of factors affecting the evaluation accuracy. Therefore, a dynamic load margin analysis method for active distribution network planning is proposed. The distribution network is reconstructed, the closing and opening operations of sectionalizing and interconnection switches are adjusted, and the fault nodes are isolated. The TSC calculation model is established according to the openable capacity, the interconnection relationship of multi feeder networks and the power flow equation, which accurately calculates the voltage drop and network loss. The forward push back method is used to calculate the power flow of distribution network, and the generalized gradient method is used to solve the TSC model of nonlinear programming, so as to achieve the goal of high quality of solution and feasible calculation results. The result of example analysis shows that this method can accurately evaluate the TSC of distribution network, fully tap the potential of distribution power supply, and reduce the total loss of feeders, which is conducive to the smooth recovery of power loss load.