The calculation of line loss for complex distribution network with distributed generation has new features.However,the traditional method cannot meet the demand for future distributed generation systems.In this paper,the radial distribution network with distributed generation is investigated.The common distributed power nodes are divided into PQ,PI,PV and PQ (V) types.According to the characteristics of each node type,the improved algorithm of forward and backward for power flow calculation is put forward.The voltage line loss is calculated for taking the system with 33 nodes as an example.Compared with the traditional distribution network,the system voltage is reduced for the distributed generation using asynchronous generator as the interface,while other interface forms play supporting roles to system voltage.