Based on the full investigation on the present situation of water environment, water environment function, and the water pollution load, Linhai City, a typical hilly area city, was chosen in this study for improving the water environmental quality in hilly area. In this study, we established the water quantity and quality mathematical models, calculated the water environmental capacity of the river net, and put forward the water pollution total quantity control and water pollution reduction plan for Linhai City. Results show that the water environmental capacity of COD and NH₃-N in Linhai City is 15 904. 3 tons per year and 1 585. 2 tons per year, respectively. The over-limit ratio of water quantity is 15. 61% for COD and 16. 67% for NH₃-N. After the project is completed in the planning year, the increase of the water environmental capacity will be 1 137. 7 tons per year for COD and 114 tons per year for NH₃-N, the water pollution reduction flowing into the river net will be 10 610. 6 tons per year for COD and 1 082 tons per year for NH₃-N, and the water environmental quality of Linhai City can be improved.