In view of the supply capacity, water resource can be divided into controllable water resource and uncontrollable one, based on the analysis of the source and the formation process of the available water, forming a dynamic water supply model. This model, on the one hand, involves the dynamics of water resource caused by different times. On the other hand, it takes the dynamics caused by different seasons into account. In this paper, a quantitative analysis method based on this model has been put forward to evaluate a region's water supply capacity.