Dianchi Lake, the largest plateau freshwater lake in China, is an important part of the ecological security pattern in the upper reaches of the Yangtze River. In order to restore the ecology of Dianchi Lake and its lakeside, farmland along the lake has been converted to grasslands and forests on a large scale since 2008. The influence of vegetation in the lakeside on the total phosphorus concentration in Dianchi Lake is a long-term process, and it needs to be evaluated through long-term continuous monitoring data based on remote sensing. In this paper, Dianchi Lake and its lakeshore are taken as research areas. From the perspectives of spatial distribution and seasonal differences, combined with the annual change of total phosphorus load of the rivers flowing into the lake, the effect of the spatial and temporal changes of the vegetation in the lakeside on the total phosphorus concentration in Dianchi Lake from 2005 to 2018 was studied. The main conclusions in this paper are as follows: (1) In terms of the spatial variation, the multi-year average of total phosphorus concentration in the Dianchi Lake gradually decreases from the edge of the lake to the center, and it is higher in the north and south. From the aspect of temporal changes, the annual average of total phosphorus concentration in the Dianchi Lake shows a significant downward trend from 2005 to 2018. (2) The significant reduction of total phosphorus concentration in Dianchi Lake from 2011 to 2018 is closely related to vegetation in the lakeside , and the growth of vegetation has a certain degree of interception on the input of total phosphorus. (3) The results of vegetation extraction show that the area of herbs and woody plants in the lakeside of Dianchi Lake increased significantly from 2005 to 2018, and the period with the most dramatic increase in both was from 2010 to 2011. (4) Compared with the normal water period and the high water period, the NDVI of herb and woody plants has the strongest negative correlation with the total phosphorus concentration in the strongly affected area during the low water period, and the negative correlation between the NDVI of woody plants and the concentration of total phosphorus in the strongly affected area is stronger than that of herbs. This paper studied the response relationship between the total phosphorus concentration in Dianchi Lake and vegetation on its lakeshore based on long-term remote sensing data, and provided scientific basis for the ecological restoration of Dianchi Lake.