Based on the research progress of water resources carrying capacity, the relationship between system structure and function, and the evolution characteristics of water resources system, the four-dimensional structure of water quantity, water quality, aquatic habitat environment and connectivity of water resources system was deduced from the three functions of natural evolution, ecological service and social service for water flow system function. The water resources carrying capacity was characterized by this method. Based on the analysis of water resources carrying subject, object and carrying process, the describing of carrying process from the aspects of water resources carrying support, pressure and regulating force, a four-dimensional index system of water quantity, water quality, aquatic habitat environment and connectivity based on carrying process was established. The selected index system can be used to evaluate the multi-dimensional water resources carrying capacity of different basins or regions