The impact of grid-connected distributed PV generation on regional distribution network is analyzed. Based on it, considering flexible network structure under the background of active distribution network, a model calculating the permitted penetration capacity of distributed PV generation is established, with a series of static security indexes adopted as constraints. Enumeration method based on dichotomy as well as hybrid intelligent algorithm is proposed to solve the model containing single PV generation and multi PV generations respectively, which ensures high efficiency. The model and the algorithm proposed are applied in calculating, comparing and analyzing the permitted penetration capacity of distributed PV generation in several representative connection modes of medium voltage distribution network. Through the case study, the effectiveness of the proposed method is verified, some regularities are summarized, and relevant suggestions are propounded.