At present, the ecological environment construction of the Loess Plateau is facing a new social environment. Vegetation managed with ecological values such as soil and water conservation began to change towards economic-utilization value. How to balance the proportion of land used for soil conservation value and land used for economic-utilization value, and how to optimize the allocation of vegetation space is an urgent theoretical and practical problem needed to be resolved. To solve this problem, this study established a value-trade-off model of watershed development from the perspective of economy-ecology-environment coupling complex system based on grid data expression of watershed. The results showed that the established value-trade-off model could calculate the maximum development benefit of the watershed based on the trade-off between grid development profit and soil loss value, and determine the optimal area threshold of watershed area development, and optimize spatial allocation of watershed vegetation. The decision-making system could provide a reference for watershed development, and help to evaluate the rationality of past watershed development and guide the spatial optimal allocation of vegetation in future watershed development.