Carbon storage is a crucial ecosystem service, with its variations significantly impacting global changes. This study, based on corrected mean carbon density for various land use types nationwide, employs the InVEST model to assess Xi’an’s ecosystem carbon storage changes from 2000 to 2020. Identifying carbon sink and source areas quantifies the impacts of climate and land use changes. Results reveal a trend of “initial decrease followed by an overall increase” in Xi’an’s carbon storage from 2000 to 2020. During 2000-2010, the total carbon storage decreased from 95.12 Tg to 94.42 Tg, with a notable proportion (5.77%) in low-carbon optimization and carbon emission control zones. Land use changes, particularly continuous built-up land expansion, slightly exceeded climate change in contributing to the decrease. From 2010 to 2020, the total carbon storage increased from 94.42 Tg to 95.76 Tg, predominantly influenced by land use change (128.21%). However, low carbon zones remained relatively high at 4.21%, primarily located in transitional zones between the Weihe River plains and the Qinling Mountains, as well as the edges of valley water systems. These ecologically crucial regions, while important, are more fragile and sensitive, underscoring the imperative for intensified protection in the future.