In order to understand the water quality variation of Hongze Lake during the transfer period of the South-to-North Water Diversion Project, the water quality monitoring data from 2013 to 2020 of Hongze Lake during the water transfer period was evaluated, and the evaluation results were analyzed by the Daniel trend test for the annual change trend of water quality. The spatial interpolation was done to obtain the distribution pattern of water quality in each lake area, and the main pollution types of water quality were further analyzed by the principal component analysis. The results showed that the water quality of Hongze Lake from 2013 to 2020 during the transfer period was mainly qualified and lightly polluted, with TP and TN as the main exceedance factors. The water quality tended to improve over time and spatially, the water quality in the overwater area was the worst, but there was a trend of turning better, while the Chengzihu area and the Lihewa area became deteriorated. The pollution type was mainly eutrophication pollution, and the nitrogen and phosphorus nutrients had a greater impact. The main sources affecting water quality were the discharge of pollutants from river inputs into the lake and the increase of construction land that is caused by human activities, but also accompanied by occasional pollution accidents. At the same time, in time Hongze Lake showed an improvement trend to the East Line water transmission of the comprehensive water quality, it is recommended to further strengthen the relevant pollution prevention work to protect the water environment of Hongze Lake and to protect the safety of the water quality of the east line of the South-to-North Water Diversion Project water transmission.