Ecological environmental issues have received extensive attention, and landscape ecological risk assessment is of great significance for regional sustainable development. Previous studies faced difficulties in accurately quantifying the impacts of land use changes and the spatio-temporal patterns of risks due to data limitations and single indicators when evaluating ecological risks in plateau areas. This led to a lack of effective bases for ecological protection and planning. This study focused on the land use types in Hainan Prefecture on the eastern edge of the Qinghai-Tibet Plateau from 1980 to 2020. Using the land use vector data, it reclassified the grassland types, analyzed the land use dynamics and transfer matrices, integrated landscape pattern indices to construct the landscape ecological risk index, and conducted spatial autocorrelation analysis. The results showed that grassland accounted for over 62%, mainly with moderate/low coverage; in the past 40 years, cultivated land and construction land expanded, while grassland decreased and landscape fragmentation intensified; the comprehensive landscape ecological risk index was approximately 0.124, mostly at medium-low risk levels; risks exhibited spatial autocorrelation with high-low aggregation characteristics. This study provides directions for plateau land use planning and risk mitigation, accurately quantifies risk patterns, facilitates the formulation of targeted ecological protection strategies, and enhances the scientific nature of regional sustainable development decision-making.