The reliability issues of the smart distribution system are studied when multiple distributed energy resources（DERs）are managed via virtual power plant（VPP）. Firstly, a VPP management strategy is proposed for power supply reliability, which includes VPP operation scheme and optimization models for each DER group. Then, reliability assessment method is developed for this cyber-physical power distribution system and the influence of the proposed strategies on power supply reliability is qualified. It is learned from case study based on IEEE 33 bus system that distribution network with faults can operate more economically and reliably via optimal dispatch of VPP. Therefore, VPP is one of the most potential platforms for the improvement of power supply reliability in the future.