Abstract: The multi-objective optimal operation and decision-making of cascade hydropower stations is always a key problem in hydropower dispatching. In this paper, an objective adjacent scale optimization model was constructed by introducing positive and negative ideal point to deal with multi-objective optimization efficiently; The genetic algorithm coupled with complex operation constraints processing strategies was used to solve the model. As a result, the optimal solution set of different target weight coefficients was determined. Based on the results, a method of multi-objective decision making based on the principle of marginal analysis of economic was proposed, which introduces marginal revenue and marginal cost to characterize the relationship between target function values of peak load regulation and navigation with the change of weight coefficient. According to the law of economic profit maximization, the marginal analysis of the weight coefficient was carried out, finally the revenue-dominating area, the cost-dominating area and the equilibrium area were determined, which give the multi-objective decision making basis. Taking cascade hydropower stations in the lower reaches of the Langcang River as the background, the model simulation test was executed in this paper. The feasible results show that the proposed method can meet the demands for multiple objectives, and lessen the subjective assumption of the traditional multi-objective decision making method.