Abstract: The paper aims to promote grain production and increase agricultural income, realize the optimal allocation of water-soil-crop in Sanjiang plain. We established a linear programming model with generalized agricultural water resources (i.e. blue water and green water) as constraints based on the actual condition of agricultural production with both rain-fed and irrigation practice by using the software LINGO 17.0 to solve the objective function and the corresponding planting area of rice, corn, soybean. The results showed that: based on the situation of 2015 and the optimization results of planting structure after the implementation of the Sanjiang Connected Project, the rice planting area increased, the corn planting area reduced significantly, and the soybean planting area had both increase and decrease. The Sanjiang Connected Project provides important facilities for the realization of water-soil-crop optimal allocation and the planting structural adjustment of rainfed and irrigated agriculture in the region. Continuous optimization of planting structure and promotion of water-soil-crop optimal allocation are of great significance for further improving the grain production capacity in Sanjiang plain.