Abstract: With the increase of distributed generation(DG) in distribution networks, the impact of these DGs in the power grid is also increasingly significant. In particular, with the development of intermittent DG which is more difficult to predict power generation, it challenges the reliability of the power grid. According to the characteristics of the grid with DG, this paper simplifies the distribution network to a system which takes autonomous control units(ACU) as the main component. Then the power grid is divided and classified into autonomous control regions(ACR) and calculates the reliability indices of different classes of ACR. And through the reliability index to establish an optimization model, eventually configure the system's DG capacity and improving the system's reliability.