The carbon dioxide generated by building sector accounts for approximately 30% of the total CO2 emissions in China. The building sector plays a significant role in Chinese low-carbon development. This study develops the CAS bottom-up model system to predict the future trend of.carbon emissions in China's building sector. Firstly, we sets three scenarios: business as usual (BAU), policy scenario, and synergistic emission reduction (SER) scenario, which consider the influence of low-carbon building policies and emission factors (i.e. power and heat emission factor (PEF and HEF)). Then we develop an emission reduction potential model to assess the CO2 abatement potential of the building sector in 2016-2050. The results reveal that low-carbon policies of building sector in policy scenario can only slow down but not curb the CO2 emission completely. The CO2 emissions will reach its peak before 2030 in the SER scenario, taking into account the impact of PEF and HEF. The analysis demonstrates that the synergistic reduction effect of inter-department will be better than that of one sector. Furthermore, green buildings, renewable energy building and energy conservation policies for district heating have a great influence on emission abatement in the building sector.