Quantifying and mapping the carbon sequestration of urban green spaces (UGSs) play a critical role in the scientific management of these areas and in enhancing their capacity to mitigate the impacts of climate change. However, the process of quantifying carbon sequestration in UGSs is complex, requiring the collection, analysis, and visualization of multi-source heterogeneous data. Therefore, it is essential to develop a digital twin (DT) platform tailored for carbon sequestration estimation, enabling automatic data integration, measurement, updating, and visualization. This study compares the advantages and disadvantages of WebGIS and ArcGIS secondary development frameworks, ultimately selecting WebGIS for constructing the DT foundation of UGSs. The research establishes the overall framework of the DT platform, the data flow framework, and the carbon sequestration estimation framework based on DT technology. These outcomes clarify the logic behind the intelligent estimation and visualization of carbon sequestration and carbon density across multiple scales of UGSs. By adopting an open-source development strategy, the proposed solution reduces software costs while providing users with capabilities for intelligent estimation and in-depth analysis of carbon sequestration. This approach enhances the level of intelligence in the research and management of carbon sequestration in UGSs.