A mathematical model for deploying distributed generation is proposed to consider overall economic performance， reliability and environment assessment at the same time， by calculating annual generation costs， the consumer's economic loss of power outage and environment protection costs. Loss of load probability is used to evaluate the reliability of power supply. Different optimal deployment scheme for distributed generators are given under different reliability targets. The sensitivity of different consumer's outage loss is also analysed. Meanwhile， environment influence of distributed generators is considered in the optimization evaluation process. Research on SO2 ， NOxemission characteristic of different kinds of distributed generators is given and deployment results under different environment protection costs are analyzed. Simulation results indicate that this model can evaluate the performance of distributed generators comprehensively and establish optimal deployment scheme which can satisfy consumers' different demands for reliability and environment protection.