This article proposes an accounting model of carbon emissions of construction materials products by a careful analysis of related researches of carbon emissions accounting of construction materials products in the world. Especially, this paper makes a special effort to analyze the source of construction materials products' carbon emissions in different stages. Also, the calculating methods of carbon emissions in different stages are defined in this paper. And autoclaved fly ash brick is taken as an example to verify the calculating methods. Then the outcome reveals that the analysis of carbon source of construction materials products and the corresponding calculating methods are feasible. Simultaneously, the impact of production technology on carbon emissions of construction materials products can be determined through the calculating. Moreover, special improvements can be put forward to optimize the production technology of raw materials of construction materials products. By doing the research in this paper, it is hoped that the research has its significance to the future study of accounting of carbon emissions of building materials.