At present, the prefabricated building has been vigorously promoted by the government, but its high incremental cost is the main obstacle to its development. Therefore, it is very important to study and reduce its incremental cost. Taking the example of two projects completed by MCC Changtian property Co.,Ltd in Changsha city, the author counts the specific data of incremental cost, analyzes the composition of incremental cost, and puts forward the measures to reduce incremental cost. The study shows that the incremental cost of prefabricated buildings can be effectively reduced by the following measures:the government should formulate and improve the norms and standards system of each link in the life cycle of prefabricated buildings,strengthen the standardization of prefabricated building design,implement the integrated contracting mode of prefabricated projects,and strengthen the management level of the whole process of design, production, transportation and installation of prefabricated building components.