Abstract: The main reason for the loop closing failure of distribution network is the overcurrent causes current protection action during the loop closing of distribution network. Firstly,a multi-voltage loop closing operation failed example due to the large closing loop surge current is analyzed. It establishes the reasonable model of the closed loop of distribution network. It obtains the calculation method of the steady loop current and analyses the transient process of decay. It is found that the key reason for the loop closing failure is not the voltage difference on both sides,but the ratio of transformation between the closing loop power flow and ring generator transformer,the transformer impedance value,the main transformer load flow and loop circuit impedance,and line load condition. Finally,the measures to improve the success rate of loop closing and breaking operation is proposed.