In order to avoid generating large loop current and impact current which would make circuit overload, closing loop operation must execute under the guide of analysis and calculation. Closing loop operation in distribution network involves transmission network, whose measurement data may be incomplete when they are obtained by the distribution network. Based on whether the closing loop involves transmission network, the paper classifies the loop into two kinds. When dealing with the calculation of closing loop involving transmission network, the paper classifies the combination of measurement data of the transmission network into three different situations, and then provides specific model and analysis for each situation. The paper comes up with the equivalent network to simplify the looped network, introduces the method for calculating the loop closing steady-state current and impulse current, and brings up the thought and process for the analysis and calculation of closing loop operation, which provide the theoretical support for the closed loop operation software.