As a distribution system possessing distributed generations（DSDGs）with flexible fault reconfiguring capability makes it impossible to use the conventional analytical algorithm for reliability evaluation，a probability calculating formula for a load acquiring supply by backup sources is derived by taking into account the randomness of wind generators，solar generators and loads. Then a new method for fast reliability evaluation of DSDG is proposed with the network reconfiguration and the probability calculation of a load supplied by backup sources taken into account. A reliability evaluation for different reconfiguration schemes based on the PG&E69-bus system in USA is performed by the method. The results have proved the correctness of the theoretical analysis and the ability of the method proposed to comprehensively and quantitatively evaluate the reliability of a DSDG，thus providing the self-healing control scheme formulation and evaluation with theoretical basis.