The construction industry has played an important role in reducing carbon emissions. Various policies have been implemented to stimulate construction enterprises to reduce carbon emissions, but the effects of emission reduction are not obvious, for they do not directly benefit the enterprises. This paper employs a modified Shapley value method to study benefit allocation in a construction supply chain considering carbon emissions. Four correction factors are proposed for modifying the initial allocation, namely the contribution rate of inputs, the risk-sharing coefficient, the degree of cooperation and the contribution rate of carbon emissions. We analyze carbon emissions based on an illustrative example of a concrete supply chain consisting of a cement manufacturer, a concrete manufacturer and a construction enterprise, and present our findings. First, the enterprises intend to cooperate to achieve the greatest benefit, and second, the benefit allocation is greatly affected by carbon emissions. Participants that produce more carbon emissions have higher carbon tax costs, which reduce profits. Further suggestions are also presented, which may help enterprises reduce carbon emissions. And policy makers should arrive at a suitable level of carbon tax to promote the smooth progress of projects and to improve the emission reduction effect.