With the continuous growth of low-carbon economy and people’s increasing preference for low-carbon products, the building carbon emission reduction (CER) has been highly concerned by the government. Therefore, in this study, we establish a game model through differential game to analyze the impact of government policies on building’s CER. We get: (1) Compared with the carbon tax policy, the government policy combining carbon tax and cost subsidy is more conducive to reducing carbon emissions; (2) For the three government policies, when the cost subsidy rate is lower than a fixed value, the government policy combining carbon tax and cost subsidy is the optimal strategy for building’s CER. When the cost subsidy rate is greater than a fixed value, the cost subsidy policy is the best strategy for building’s CER.