Traditional fault analysis of distribution networks cannot meet the requirement of distributed generation system（DGs）. In order to solve this problem， different distributed generators are classified into four types: PQ node， PI node， PV node and PQ（ V） node. According to the properties of four types of nodes， different methods are proposed to handle different types of nodes in fault calculation. Considering the asymmetric property of three-phase distribution networks with DGs， based on the forward and backward method， superposition principle with fault compensation circuit is used in fault analysis under an unified formula and similar iteration process as load flow calculation. The proposed approach can deal with both radial structure networks and weakly coupled circle networks. Test results of 13-node test system verified the feasibility and effectiveness of the proposed method.