Abstract: The concept of region water resources carrying capacity (RWRCC) is developed, the connotations and essence of RWRCC are revealed, RWRCC is considered as having the characteristic of "liquid", i.e., in a given status, RWRCC is fixed, but the representations of RWRCC can be various.The model for calculating RWRCC is established by taking the "carrying population" as its integration index and using the system optimizing method.The status quo of RWRCC in Tianjin area is calculated and analyzed approximately.