Formwork engineering is one of the major cost factors in reinforced concrete construction, which is not only critical for the successful completion of construction projects, but also critical for profitability. The traditional formwork design process includes waste, resulting in non-value-adding manpower and operational time. The purpose of this research is to utilize lean thinking in formwork design so as to enhance design correctness and eliminate waste. A lean design process for formwork engineering is established to achieve this goal. In the design process, design correctness is established to review and correct design errors. An organizational learning environment is thus built. The proposed lean design process is conceptualized using stock-flow diagrams. This research validates the applicability of the proposed approach using a real case. Application results show that the proposed method can reduce wasteful manpower and operational time in formwork engineering.