In this paper

in allusion to the three kinds of serious overvaluation (the budgetary estimate of project construction exceeds the rough estimate

the budget exceeds the budgetary estimate and the final accounts exceed the budget) causing uncontrollable project investment often appeared in domestic project construction

the main causes for that are analyzed. That is

the frequent project change and the malpractice of the cost managing system. In this paper

according to some real projects

the kinds and causes of project change are clarified and the malpractice of the cost managing system is analyzed. The effective approaches of reducing the project change

especially the united surveying and improving the cost managing system in order to make the effective control of the project investment are realized.