Safety inventory quantity computation based on Collaborative Planning Forecasting & Replenishment (CPFR) can avoid uncertainty of material supply in building construction, which can also coordinate relationship between supplier and construction side to reduce inventory cost and to ensure the progress of construction. The paper analyzed systematically on relationship between lead time and safety inventory. Combining with application of CPFR and based on establishing good relation between material supplier and construction contractors, safety inventory level was reduced with management of lead time. Supply of material supplier was also coordinated to reduce uncertainty of inventory quantity. Construction application example based on improved safety inventory quantity method also proves the feasibility of the proposed method.