Building carbon emissions (BCEs) from the construction industry are crucial to realizing the ‘Dual-Carbon’ Goals of China, but their spatio-temporal and stage differences are not fully understood. Here, we explored the spatial and temporal differences of building carbon emissions in the Yangtze River Delta urban agglomeration by combining life cycle assessment and spatial analysis, and further compared the contribution rates of each influencing factor to BCEs based on the LMDI-STIRPAT model. The results revealed that from 2005 to 2020, the growth rate of building carbon emissions in the Yangtze River Delta urban agglomeration slowed after 2013, with a spatial trend of ‘slow in the east and fast in the west’. With respect to the whole process, the contribution of building materials production and transportation to BCEs is the most significant. Additionally, the types of building materials and energy used in each stage have changed dramatically over the 16 years. Furthermore, GDP per capita and carbon intensity are the strongest positive and negative drivers, respectively. These findings provide a complete understanding for a regional exploration of BCEs and contribute to formulating low-carbon building policies within urban agglomerations.