Enhancing the carbon sequestration capacity of ecosystems in key regions, such as Chengde City, is crucial for achieving China’s long-term goal of carbon neutrality. This study innovatively applies a comprehensive evaluation model to quantitatively evaluate the spatio-temporal disparity and key factors influencing the ecosystem carbon sequestration capacity in Chengde City over two decades, aiming to provide a solid scientific foundation for local policy formulation and to explore effective strategies for enhancing regional carbon sequestration potential. Based on Land Use and Land Cover Change data from 2000 to 2020, the study employs the carbon sequestration factor method from the “2006 IPCC Guidelines for National Greenhouse Gas Inventories” to quantitatively analyze the carbon sequestration ability of various kinds of ecosystems. Quantitative analysis revealed a 0.56% decrease in the annual carbon sequestration of Chengde’s ecosystems from 17.8215 million tons in 2000 to 17.7214 million tons in 2020, indicating an average annual reduction of 0.0501 million tons. Forestlands and cultivated land, which are primary contributors to carbon sequestration, account for over 80% of the total capacity. Spatial distribution analysis identified Fengning County, Weichang County, and Longhua County as the areas with the most concentrated carbon sequestration capacity, together accounting for over 60% of Chengde’s total annual carbon sequestration. The continuous decline in Chengde’s ecosystem carbon sequestration capacity was closely linked to changes in land use, accelerated urbanization, and rapid economic development. To counteract this observed decline, the study recommends strengthening the construction and management of ecological conservation areas, holistically promoting sustainable agricultural practices, systematically advancing urban greening projects, and actively raising public environmental awareness. These comprehensive measures are expected to optimize land resource utilization, enhance the carbon sequestration functions of ecosystems, and improve ecological security and residents’ quality of life, thereby providing robust support for the sustainable development of Chengde and its surrounding regions.