Abstract: Xingkai Lake is the largest freshwater lake in northeast Asia, and its excessive concentration of total phosphorus (TP) is the main reason for the decline of water quality in Xingkai Lake in recent years. Climate change may have an important impact on regional water quality decline. Taking Chinese region of Xingkai Lake as the research area, by analyzing the temporal and spatial variation characteristics of phosphorus in the water body of Xingkai Lake, the main composition and morphology of phosphorus in the water body of Xingkai Lake were explored, and the change law of climate factors in the region and its influence on TP of the water body of Xingkai Lake were clarified. The results showed that: (1) From 2010 to 2021, the overall TP concentration change in Xingkai Lake showed a trend of first decreasing and then rising, and the water quality of Xingkai Lake in the freezing period was better than that in the non-freezing period, and TP concentration in Great Xingkai Lake was higher than that in Small Xingkai Lake. (2) The phosphorus morphology data in May 2022 showed that the TP of the water bodies in Great Xingkai Lake and Small Xingkai Lake was mainly composed of granular phosphorus (PP) (accounting for 60% and 76%, respectively), which was the main form of TP exceedance. Both the granular phosphorus and dissolved phosphorus in Small Xingkai Lake were higher in the north and lower in the south. For Great Xingkai Lake, the granular phosphorus was higher in the east than in the west, and the dissolved phosphorus showed the opposite trend. (3) In recent years, both temperature and rainfall had shown an upward trend in Xingkai Lake basin, and TP in Great Xingkai Lake had a significant positive correlation with temperature and rainfall, the increase in temperature and rainfall may lead to more nutrients entering the water body, resulting in a decrease in the quality of the water environment. There was no significant correlation between TP of Great Xingkai Lake and climate change, but there was a significant positive correlation between TP of Great Xingkai Lake and Small Xingkai Lake, indicating that Great Xingkai Lake was less affected by regional climate change, but its water quality condition was closely correlated with Small Xingkai Lake. The water quality of Small Xingkai Lake was better than that of Great Xingkai Lake no matter in the freezing or non-freezing period, and as the antecedent reservoir of Great Xingkai Lake, Small Xingkai Lake played an important role in purifying the surface source pollution in the upper watershed.