To solve the safety problems caused by immature technology， insufficient talent reserves and many other problems with the current assembly building， we use the Delphi method combined with expert opinions to select five primary indicators of personnel， environment， management， equipment and technology， and their 19 secondary indicators to construct， based on the improved AHP-FCE method， a risk assessment system for assembly building safety. We determine the influence coefficients of each indicator and compare and rank them， refine the key factors that affect the safety of assembly buildings， and empirically analyze the risk of an assembly building project''s safety in a certain place. The results show that， according to the improved AHP model calculation， the construction organization and design and the construction plan， the prefabricated components'' quality， and the accuracy of node connection are the major risk factors for assembly buildings， with proportions of 0.302， 0.203， and 0.141 respectively. Further， we empirically evaluated a field project with the FCE method， and it''s at a relatively lower risk level. Our study multi-dimensionally reveals the risk factors for assembled buildings'' safety， and provides references for the safety management of field projects.