Abstract: In order to understand the impact of the requirements of upgrading the effluent quality standards on the cost, we proposed a system to classify the effluent discharge limits of municipal sewage treatment plants. We synthesized current national and local discharge standards of municipal sewage treatment plants, and classified the discharge limits of major contaminants present in wastewater into four levels, namely grade 1-A of Discharge Standard of Pollutants for Municipal Waste (GB 18918-2002) (level 4), quasi grade V of Environmental Quality Standards for Surface Water (GB 3838-2002) (level 3), quasi grade Ⅳ (level 2) and quasi gradeⅢ (level 1). Then, we assessed the technical and economic feasibility of upgrading the effluent discharge level from level 4 to level 3, 2, and 1, respectively. We found that the cost and floor area were greater from (level 4→level 1) > (level 4→level 2) > (level 4→level 3) when the discharge concentration limits were upgraded for a 10×10⁴ t/d municipal sewage treatment plan. When upgrading discharge quality from level 4 to level 1, the investment cost increased by 1.1×10⁸-1.4×10⁸ RMB, operating cost increased from 1.6 to 1.8 RMB per ton, and the floor area increased by 2000 m². Taking a medium-sized city in China as an example, the maximum investment cost increased by 24.4×10⁸-31.1×10⁸ RMB, operating cost increased by 13.0×10⁸-14.6×10⁸ RMB per year, and the floor area increased by 6.8×10⁴ m². Our results indicate that the effluent of municipal sewage treatment plants can be directly linked to the goal of improving water quality, which will drive the costs of treatment up substantially.