Forest carbon sequestration is crucial for mitigating global warming and promoting the realization of China's carbon neutrality goal. Using the optimal price method, carbon tax method and afforestation cost method, the forest carbon sink value of 12 league cities in Inner Mongolia from 2009 to 2023 was evaluated and its spatiotemporal evolution pattern was analyzed. The index system was constructed from the four dimensions ofeconomy, society, nature, and scale, and the spatial econometric model was used to reveal the influencing factors, correlation characteristics and spatial spillover effects of forest carbon sink value. The results showed that: ①Over time, the forest carbon sink value of Inner Mongolia showed an increasing trend,with faster growth rates in eastern and central Mongolia. Spatially, the overall spatial pattern was "high in the east and low in the west". ②The forest carbon sink value of Inner Mongolia had a significant global spatial correlation and the degree of spatial agglomeration was not constant. The low-low correlation league cities were Alashan League, Bayannaoer City and Wuhai City; while the high-low correlation league city was Hulunbuir City; and the Xing'an League showed alternating low-high correlation and high-high correlation. ③There is a significant positive spatial spillover effect among the leagues and cities. Specifically, for every 1% change in the forest carbon sequestration value of neighboring leagues or cities, the corresponding value in the local area changes in the same direction by 0.205%. The level of urbanization positively impacts forest carbon sequestration value, primarily influencing local forest carbon sequestration. In contrast, factors such as labor input, local government fiscal expenditure, and forestry management levels exhibit a negative impact on the forest carbon sequestration value of neighboring leagues or cities. The results of this study provide an important reference for in-depth understanding of the internal mechanism of forest carbon sink value change, and promoting the realization of forest carbon sink value and sustainable management.