For the specific situation of Inner Mongolia, use of small isolated power generating system of wind power-led to provide electric energy, can ensure reliability, saving diesel fuel and protect the local ecological environment. In this paper the small isolated power systems was described as Wind / diesel / storage power generating system. This Article use sequential Monte-Carlo simulation method to evaluate the system reliability. According to the historical data of wind farm, establish the wind speed time series model, than calculate the output of WTG. Considering the units random failure, use generator and load models to obtain the battery time series model. To a sample system, quantitatively assessment a number of factors that affect the system reliability, such as the simulation sample size, the battery capacity, the battery charging and discharging rate and the WTG rated power and so on. The simulation results can provide basis for the wind / diesel / storage system reliable operation, and for the government and the power sector to promote wind / diesel / storage co-generation system to remote areas.