The water environmental carrying capacity (WECC) of a city can demonstrate a balance between the level of exploitation of the local water resources and the population growth and concomitant socio-economic development. To begin with, the definition of WECC was elaborated. Combined with hydraulic, hydrologic and water quality data, a one-dimensional water quality model was subsequently applied to simulate the water pollutants (chemical oxygen demand (COD)) in Tieling City. Then, a multi-objective model was applied to explore WECC. Economy, demography, and contaminant were selected as goals, taking into account the constraints of macroeconomic aggregates, water supply, water quality, and population. The results showed WECC could nearly carry all planned gross domestic product (GDP), population in the planning years 2015, 2020, and 2025 with the maximum COD of 30,681.7 t, but not for the condition of maximum COD of 15,709.0 t. That is, COD overload would occur if GDP and population develop as planned. Some measures must be taken to improve WECC in Tieling City, which are valuable for supporting the adjustment and planning for social-economic development.