Abstract: The refined and optimal allocation of water resources is an important means for the sustainable utilization of water resources. Describing the high spatial complexity of water resources system and the time-varying characteristics of water command and supply elements accurately is an important and difficult problem to be solved in establishing the refined and optimal allocation model of water resources, which has not been well solved at present. In view of this difficulty, this paper establishes a refined and optimal allocation model of water resources in the basin on two scales of space and time. At the same time, it also considers the influence of reservoir storage requirements, evaporation and leakage loss, backwater relationship between water command and water supply nodes on the accuracy and applicability of the model. The water supply units and water command units in the basin are classified, and the constraint conditions are established for different types of units. Taking the minimum water shortage as the optimization criterion, the refined and optimal allocation model of water resources in the basin is established and solved by linear programming. The conclusions of the practical application in Nanpanjiang River Basin are as follows:（1） the satisfaction rate of rural water and urban water in the basin is 100%, the satisfaction rate of agricultural water is 97.7%, and the satisfaction rate of industrial water is 82.4%. Considering the requirement of reservoir impounding at the end of the year and the restriction of pipeline, some agricultural and industrial water consumption joints are short of water, and fine allocation on two-way scale of time and space has been realized on the whole.（2） The total evaporation loss of Heitan Reservoir accounts for 6.6% of the initial reservoir capacity, and the monthly total backwater flow in agricultural water consumption of Bailang Irrigation Film accounts for 25% of the actual water flow, which indicates that factors such as evaporation leakage loss of reservoir and backwater flow have an important influence on the optimal allocation of water resources.（3） The model accurately describes the complex relationships among the nodes in the water resource system, which can provide a guidance for the scheme formulation of optimal allocation of water resources in complex watershed.