In view of the previous studies on uncontrollable construction cost, which mostly were based on the practical experiences and subjective speculating, the conclusions were empirical and lack of data support. In order to solve this problem, the quantitative analysis methods are introduced here. The application of ABC analysis method can distinguish the minor-key factors from tremendous factors which influence the cost changes. And the complete decomposition of construction cost changes can

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... se the main effects of the cost changes to define the key effects. Through applying these two methods, the construction cost can be controlled by mainly controlling the key factors and effects of the projects. Besides, project data of uncontrollable construction cost can be accumulated to provide objective and scientific suggestions on controlling cost. A completed small civil engineering is presented as an example.