Most current water allocation strategies fail to address the unbalanced development among multiple systems. How to optimize the coordination development relationships among the social, economic and environmental systems has always been the focus. To bridge this gap, a water optimal allocation model for coordinated development was innovatively constructed and applied to the main stream of the Xiangjiang River Basin, China. The results showed the following. (i) From 2025 to 2030, the water deficit ratio of the study area will increase from 3.21 to 5.50% when P = 50% and from 4.59 to 6.85% when P = 75%. The existing water supply capacity will not be able to meet the increasing water demand. (ii) Agricultural and industrial water will account for a large proportion of the total water consumption. Due to the transformation of industrial structure, measures should be formulated to bring the best benefits. (iii) Restricted by different systems, the coordinated development in each city will present spatial and temporal differences. (iv) The proposed model was proved to overcome the backwards of uncoordinated development and achieve a balance of the regional social, economic and environmental benefits. Also, some recommendations and limitations were discussed. This study provides an effective basis for enhancing regional sustainable water resources planning and management.