The use of metal nanometer film coupon can effectively reduce the long term test period and the operator error in selection of storage or display materials in museum, and the digital analysis of metal nanometer film coupon can avoid the human caused error. In this paper, the circular metal nanometer film coupon is detected first, and then corroded images is segmented and the are using K-means clustering algorithm is calculate. The classification results compared with that of human beinas made and results are found almost the same. It is demonstrated that the proposed method can evaluate the materials used in museum collections storage and display rapidly and accurately.