Abstract: Prefabricated building structures and steel structures are both the main forms of current building construction, and they are also the main directions for future building development. Therefore, in the development process of modern construction engineering, efforts are being made to study the prefabricated steel structure of buildings. The research object of this paper is the calculation criterion of prefabricated assembly rate of prefabricated steel structure building, and adopting the national assembly rate calculation standard, Beijing calculation standard, Shenzhen calculation standard, Shanghai calculation standard and Jiangsu calculation standard. The calculation standard is used for comparison, and a new type of steel structure precast assembly rate calculation standard is also proposed. The results of this experimental study show that the calculation method of the new precast assembly rate is more accurate than other calculation methods. The application of surrounding furnace structure and interior parts is more reasonable and effective.