Fuxian Lake, the largest deep freshwater lake in China, has experienced increasing ecological pressure due to rapid urbanization and tourism development. This study investigates the spatiotemporal impacts of land use change on ecosystem carbon storage in the Fuxian Lake Basin, aiming to support sustainable land management under global environmental change. Using land use data from 2010 to 2020, the PLUS model was applied to simulate land use patterns under three development scenarios projected to 2030. The InVEST model was then used to quantify corresponding changes in carbon storage. Results show that between 2010 and 2020, cropland areas significantly declined (−362.7 hm2) while construction land expanded rapidly (+427.3 hm2), contributing to accelerated carbon loss, especially in the northern plains. Scenario-based projections indicate continued land development and ecosystem degradation, with the “Policy Protection” scenario resulting in the smallest carbon storage loss (5.25 million tons). This suggests that targeted spatial regulation can play a critical role in mitigating ecological degradation and preserving ecosystem functions. The study highlights the utility of integrated land use and ecosystem modeling for informing ecological management strategies in sensitive lake regions under intensifying human activity and environmental stress.