From the perspective of cost-benefit analysis, an optimal configuration model of microgrid power supply based on maximizing net benefits is proposed. Firstly, a calculation model of annual net benefits is built. This model takes overall consideration of costs of equipments, operation and maintenance, fuels, as well as benefits of energy saving, emission reduction, loss reduction, reliability improvement and delay of power grid investment. Then an optimization model is proposed with the objective function of annual net benefits and constraints of charging and discharging of energy storage units, adequacy under isolated island operation in the whole year and carbon emissions. Using the genetic algorithm to solve this model, the results show that configuration schemes obtained by this model can ensure best economy of investments and provide a theoretical basis for the planning and construction of microgrid.