Since the enactment and implementation of GB/T 50378 of Green Building Evaluation Standard, the green building has been developing rapidly in China. Nowadays, with the continuous updating of standards, new technologies, new products and new applications also emerge continuously, leading a better enforceability of green buildings. In the developing process of green architecture, the development enterprise will pay great attention on controlling the incremental cost. However, limited by the specialty knowledge and understanding deviation, there is a certain misunderstanding about incremental cost of green building. This paper explains how to calculate the incremental cost of green building correctly from the perspective of green building declaration, so as to guide people to look at the incremental cost of green building objectively, and also to be beneficial to the benign development of green building.