Abstract: Landscape pattern and its vulnerability have direct impacts on ecological environment in the basin. In order to protect the ecological security in Nansihu Lake basin, we analyzed the changes of landscape pattern based on seven sets of land use data (1980-2015), with landscape adaptability index (LAI) and landscape sensitivity index (LSI) being used to build the landscape vulnerability index (LVI). The spatial distribution and changes of LVI were analyzed. Results showed that the percentage of arable land areas decreased by 4.6% and construction land areas increased by 39.7% from 1980 to 2015. Other land use types showed fluctuating changes. The areas of forest land, grassland, and unused land decreased while water area increased. The arable land was the dominant land use type from 1980 to 2015 in this area. The degree of fragmentation of arable land and water area in the basin increased, whereas other land use types decreased. The fragmentation of whole basin decreased, but connectivity among landscape types enhanced. The irregularity and complexity of landscape pattern decreased, but diversity and evenness of landscape pattern displayed an increasing trend. With respect to LVI in different periods, the eastern part of the basin was higher than the western part, while the northern part was higher than the southern part. The spatial distribution of LVI was related to topography, layout of landscape types and change of land use. The LVI of Nansihu Lake basin showed a decline trend during 1980-2015. In the eastern part of the basin, higher level of LVI gradually dispersed and was replaced by lower level. In the northwest, the recovery of LVI was obvious. In the south and southwest parts, LVI was consistently low.