Abstract: In order to speed up water circulation and exchange in Caohai Lake and improve water quality in the lake, a series of projects were implemented in succession, including Niulan River-Caohai emergency water supplement project, water eco-compositive purifying project in old and new Yunliang River, Haigeng bank water replacement channel project, and Xiyuan tunnel project, all of which provide necessary water resource for sewage interception and separated drainage. As a result, the sewage and clear water in the lake area is separated and water exchange cycle is shortened. The results of coordinated operation of projects show that: ① there is a significant linear correlation between water quality of the clear water area of Caohai Lake and water from the Niulan River, and TP concentration is mainly affected and determined by the water coming from the Niulan River while TN is influenced by the quality of water coming from the rivers in the lake basin; ②the water quality in clear water zone is highly correlated with the water discharge quantity coming from Xiyuan tunnel project, and it tends to be well improved as discharge quantity goes up; ③the appropriate water replenishment by Niulan-Caohai project is suggested as 3.0 m3/s; although Haigeng bank water replacement channel project helps maintain a favorable water landscape, the water coming from the Niulan River should be discharged by Xiyuan tunnel so as to give full play to the comprehensive benefits of Caohai water pollution control projects.