Abstract: The concentration of COD_Cr, TP, TN, and NH₃-N of Yangzonghai Lake in 2019 to 2020 was calculated. They all tended to be decreasing, which indicated that the water quality of the lake was becoming better and better that would reach the second class of the national water standard. The concentration of TN and NH₃-N showed significant correlated on the 0.05 level based on the Pearson correlation coefficient method. The other two indices had insignificant correlation. The changes of concentration in the arsenic polluted sites demonstrated significant correlation. The concentration of TN and NH₃-N was obviously impacted by the flood. It was low in the flood season.