Abstract: Under the background of China’s carbon peaking and carbon neutrality goals, clarifying the spatiotemporal evolution of carbon storage and its driving mechanisms in the Lishui River Basin is of great significance for enhancing regional carbon sequestration capacity and optimizing territorial spatial patterns. In this study, an integrated intPLUS-InVEST framework was employed to systematically analyze the spatiotemporal evolution of carbon storage in the Lishui River Basin from 2000 to 2020 and to predict future carbon storage under different development scenarios in 2040. Meanwhile, the Optimal Parameters-Based Geographical Detector (OPGD) was used to identify the key drivers of spatial differentiation in carbon storage. The results showed that: 1) significant changes occurred in land-use structure from 2000 to 2020, with continuous decreases in cropland and grassland, while forestland, water bodies, and built-up land generally increased; 2) carbon storage exhibited a fluctuating trend characterized by a decline-increase-decline pattern during the study period, although the overall magnitude of change was relatively small; 3) land-use conversion was an important driver of carbon storage change, with forestland conversion resulting in a carbon storage loss of approximately 5.20×10⁶ t; 4) compared with 2020, carbon storage in 2040 was projected to decrease by approximately 0.64×10⁶ t, 0.28×10⁶ t, 0.75×10⁶ t, and 0.10×10⁶ t under the natural development, cropland protection, urban development, and ecological priority scenarios, respectively, with the ecological priority scenario exhibiting the smallest decline; and 5) transportation accessibility and topographic conditions were identified as the dominant factors affecting the spatial differentiation of carbon storage. Among them, the distance to highways, slope, and distance to secondary roads showed relatively high explanatory power, while the interaction between the distance to tertiary roads and annual precipitation exhibited a significant enhancement effect. The findings indicate that the decline in carbon storage in the Lishui River Basin is mainly attributed to the conversion of high-carbon-density land-use types into low-carbon-density land-use types. Therefore, strengthening ecological conservation and restoration, optimizing land-use structure and territorial spatial planning, and enhancing regional carbon sequestration capacity should be prioritized in future watershed management.