Water is essential for all creatures on the earth and the Water Environment Carrying Capacity (WECC) is a critical factor that extensively influences the pace and the scale of economic and society development. The preconditions and the foundation to protect water environment and utilize water resource include: Developing a WECC info system, analyzing the features of each factor and the interrelations among them, revealing the mechanism and condition of water environment sustainable carrying capacity, and implementing an accurate WECC assessment are. In this paper, the basic theory and the research background of WECC are firstly introduced, followed by the review and investigation on the state of the art assessment methods of WECC. Based on the systematic analysis on the features of various methods, the existing problems are proposed, and some suggestions for the further study in this area are given by the authors.