The water quality identification index (WQI) evaluation method was used to analyze the temporal and spatial distribution of water quality in the Dishui Lake in Shanghai and the rivers into the lake from August 2018 to July 2019, and analyze the main factors affecting water quality. The results show that: the water quality of Dishui Lake and the rivers into the lake are spatially different; Wailian River, Zhonglian River, Neilian River and the mouth of the lake are “medium”, and the water quality of Dishui Lake area is “good”； The water quality in the Dishui Lake area has gradually improved. The water quality parameters that are significantly related to WQI include total nitrogen, ammonia nitrogen, and water temperature; the main influencing factors of seasonal changes in water quality are water temperature and precipitation, and the main influencing factors of spatial changes are the quality of water diversion sources and human activity. According to the water quality characteristics and influencing factors of the region, the biological treatment method, the reconstruction of rainwater discharge pipelines, and the strengthening of monitoring of important indicators are proposed.