[Objective]Within the framework of the dual carbon target vision, addressing the scale effects of forest land changes and quantifying the carbon sequestration benefits at multiple watershed levels not only introduce a fresh perspective into forest land research but also aid in cording and optimizing the forest land pattern. That holds great significance in enhancing future regional carbon sequestration potential.[Methods]Focusing on Chongqing as the study area, we analyzed the spatiotemporal dynamic changes in forest land and carbon storage from 2000 to 2030 at the multi-watershed scale, utilizing PLUS model, landscape pattern indices, biomass expansion factor method and grey correlation degree. Furthermore, we explored the correlation between forest land pattern changes and carbon storage under natural development scenarios.[Results](1)Between 2000 and 2020,the forest area increased by 3404.55 km2,primarily due to the conversion of cultivated land. The forest landscape pattern in the first-grade watershed showed a tendency towards clustering and regularity, with a relatively reduced degree of fragmentation. There were distinct differences in the historical laws and future trends of forest landscape pattern changes in the secondary watershed’s “district and group”.(2)In the initial two decades, the carbon storage of forest land exhibited an increasing-decreasing trend, resulting in an overall increase. The Dongting Lake system in the first level basin witnessed the highest increase in carbon storage, and the high-value area of carbon storage increment in the seconde level basin shifted from north to south.(3)The total carbon storage is predicted to increase by 2030 which is strongly correlated with the irregular index. The scale effect leads to the spatial heterogeneity of landscape pattern change and the correlation degree between landscape pattern index and carbon storage in the primary and secondary basins.[Conclusion]The research outcome contribute to understanding the patterns of forest land changes from a cross-watershed scale perspective. This, in turn, provides a scientific foundation for the Ministry of Natural Resource or relevant forestry departments to formulate effective utilization and protection policies for forest land resources at different scales, It also supports the sustainable development of Chongqing, enhances carbon sink efficiency, and facilitates the achievement of carbon neutrality goals.