Distributed generation has the advantages of close to load center, flexible control and friendly environment. But its output needs attention for its random fluctuation and uncertainty. In this paper, the output characteristics of wind and photovoltaic power are mathematically modeled and the output probability density distribution function is calculated. The reliability of access to distributed generation is analyzed by an example. Results show that distributed generation can effectively reduce the outage time of distribution network and play a positive role in improving the reliability of power supply.