With the smart grid related technologies becoming more and more mature，formulating a complete system of microgrid reliability evaluation has become one of the most important theoretical research topics.Based on the failure mode analysis and Monte Carlo simulation method，this paper puts forward an algorithm of evaluating microgrid reliability indexes considering the influence of the random characteristics of microgenerator output.With this algorithm，the reliability indexes of load points in microgrid and of the whole microgrid system are both described.Based on it，the mechanism of load classification is introduced，and the variations about reliability indexes of customers and microgrid system in different classification methods are analysed.On that basis，some load classification modes are recommended.