With high penetration of distributed generation connected to the grid, distribution system will have some huge impacts, and system reliability calculation models and assessment methods are changing. Based on Monte-Carlo method, a heuristic reliability analysis method for distribution system with distributed generations was proposed in the paper, which focuses on the mode of distributed generation in parallel to system power supply. Functional role of distributed generation in the power distribution system failure and distributed power adapter with load strategies were analyzed in this method. Cases simulation analysis was used to verify its effectiveness.