The study of cost control of assembly building is of great practical significance for accelerating the promotion of as-sembly building application and enhancing the economic benefits of contractors.Based on the perspective of general contractors,a system dynamics approach is applied to construct a system of factors influencing the hidden costs of assembly buildings for analysis.The results show that the four factors of distribution and installation synergy,professional design synergy,quality of con-struction personnel and management system are the key to controlling the hidden cost,and the strategy for controlling the hidden cost of assembly building project is proposed based on the lean management idea.