Urban green spaces (UGS) are critical components which offer both direct carbon sequestration enhancement and indirect emission reduction functions. This study utilized the Improved CASA Model and various morphological indicators to explore the relationship between large-scale urban green spaces and their carbon sequestration capacity from the perspective of landscape ecology. Net Primary Productivity (NPP) was used to represent the annual carbon sequestration capacity of plants, while 13 morphological indicators were selected to examine their correlation with this capacity. The study focused on the Nanjing Main Districts as a case study. The results reveal that among the thirteen indicators, one demonstrated a strong correlation with carbon sequestration, ten exhibited weak correlations, and two showed no correlation. Specifically, the Spearman Correlation Coefficient for the Percentage of Built-up Area Patches (BA) was -0.625, indicating a strong negative correlation with the carbon sequestration capacity of large-scale urban green spaces. In contrast, the Total Landscape Area (TA) and Total Landscape Connectivity (TC) showed no correlation. The remaining indicators displayed weak correlations. This study offers a quantitative basis for further investigations into the mechanisms and principles underlying the relationship between large-scale urban green spaces and carbon sequestration capacity.