Abstract: In order to understand the characteristics of water quality changes in Yangzonghai Lake in the past 10years and the effect of arsenic control after the arsenic pollution incident, the water quality monitoring data from 2012 to 2021 were studied, and it was found that the main monitoring indicators such as chemical oxygen demand,total phosphorus, total nitrogen, and arsenic decreased significantly, and the comprehensive pollution index and comprehensive nutritional status index showed a significant downward trend, indicating that the water quality of Yangzonghai Lake has improved, and the treatment of characteristic pollutant arsenic has achieved remarkable results in the past 10 years.