Abstract: In order to study the changes of aquatic vegetation and water quality after removal of pen aquaculture in Lake East Taihu, the landsat-8 (OLI) data with 30 m resolution was selected as the data source to perform the supervised classification of aquatic vegetation. In addition, the field survey data of aquatic plants, as the basis for the classified evaluation of aquatic vegetation, was used to interprete the changes of typical aquatic vegetation in Lake East Taihu before and after the removal of net-pen aquaculture, and to analyze the changes of main water quality indexes and algal biomass from 2018 to 2020. Results show that, after the net-pen aquaculture of Lake East Taihu being completely removed in the end of 2019, the distribution area of floating-leaf plants in 2020 increased by 25.9% compared with that in 2018, and the distribution area of emerged plants and submerged plants reduced by 11.8% and 17.0%, respectively. The dominant species of submerged plants changed from erect species to canopy species. The biomass of floating-leaf plant, Trapha maximowiczii, and the canopy submerged plant, Ceratophyllum demersum, increased explosively to 6.84 and 9.90 kg·m^-2, respectively. From July to November 2020, the water transparency in the former net-pen aquaculture area was only 25.9 cm, which decreased significantly compared with the same period in 2018. The decline of transparency is not conducive to the growth of submerged plants and the maintenance of macrophyte-dominated clear state. The concentrations of chlorophyll-a and ammonia nitrogen increased significantly, implying that there is a risk of transformation to algae-dominated turbidity state in Lake East Taihu. After the removal of pen aquaculture in Lake East Taihu, the lake ecosystem has changed greatly. Therefore, it is necessary to strengthen the ecological research and management of the lake, and artificially assist the lake ecosystem to succeed to the macrophyte-dominated clear state.