To establish an analytic model for carbon emission of building lifecycle, based on life cycle theory, a generic model for energy carbon emission of building materials was proposed. With the model, building materials were classified into several categories, such as cement, steel etc. Furthermore, some product from each category, such as PS325 in cement, was selected as a benchmark of this category. And then product coefficient and region coefficient were induced to express the differences in products and regions or manufacturers. With the proposed model, generic models for cement and steel were established. And it is found that energy carbon emission intensity of steel is around 30~40 times than that of cement. Energy carbon emission of PI525 and PO425 are 51% and 34% more than that of PS325, respectively. Carbon emission of large-scale steel and cold rolling strip is the most emitter in steel products.