As the construction of grid-connected microgrids continues to advance, regional distribution network presents the characteristics of multi-level and multi-operators. In this paper, an energy management optimization strategy considering distribution network layer, microgrid layer and user layer is proposed based on Stackelberg game theory. In the external game, the distribution network as leader sets the prices, while microgrids as followers adjust their trading strategy with the distribution network. In the internal game of each microgrid, the microgrid as leader adjusts the internal price, while the user as follower adjust the electricity consumption strategy in response to the price. By applying the Karush-Kuhn-Tucker (KKT) conditions, the tri-level model is reformulated into a bi-level model, and iterative process combining heuristic algorithm and solver is adopted to solve the model. Results of case analysis verify that the proposed method can not only increase the economic benefits and realize the coordinated optimal operation of each stakeholder, but also has positive significance in improving the voltage quality of the distribution network and renewable energy consumption.