Abstract: Since the international market of rough diamond is relatively blocked，the general appraisers who are lacked of the direct reference information on trading could not evaluate the rough diamond by the traditional appraising approaches. By the analysis of the value chain and the research on the value chain of diamond，a quality-grading system based on the system of polished diamond grading is built up．The principle of cost-reverting approach is put forward and the application is introduced．On the basis of the principle and the approach，a computeraided data base technique is adopted and enable the evaluation more efficient and accurate．The principle can also be applied in the field of the evaluation on the other rough gem materials．