Microgrid provides a reliable grid connection and management platform for renewable energy power generation, including hydroelectric power generation. Its optimal operation is an important issue. Based on the concept of opportunity cost, the optimization model is established to maximize the opportunity cost of hydroelectric power in the current period, and the cost-benefit model of hydroelectric power is established as the basis of the optimization operation model. Then, the objective function of the model is established based on the economic operation cost and environmental conversion cost, and the optimal operation model of microgrid is established taking into account the power balance constraints, distributed generation operation constraints, energy storage operation constraints and other necessary constraints. Finally, the solution flow of the model is designed based on the algorithm of firefly. Finally, by setting the off grid mode and the grid mode respectively, the established model is used to make the optimal operation plan of the system, and the indicators are compared to verify the effectiveness of the established model.