Risk analysis is an important content of project risk management. The risks of prefabricated building are more complex than general constructions for the connotation of prefabricated building. A risk system was built in whole life cycle of prefabricated building, and objective system of prefabricated building was ascertained. Then environmental system risk and implementing risk were analyzed, and technology and management system factors of leading to implementing risk were further analyzed as well as the relationship between risk factors and participant body. At last, analyses on how the risk factors and participant body affect the achievement of prefabricated building objectives were conducted. These analyses can help the participant body improve understanding of prefabricated building and be prepared for dealing with the risks．