Abstract: objective: to obtain the distinct image of various pigment dermatosis, and develop The skin image analysis system with uncomplicated operation, high automatic and accuracy. Method: The parameters of measured skin lesion, such as the shape, the acreage, the integrative optical density and changes of pigment etc were detected by poly spectrum polarized light and digital image analysis system. Results: 136 cases of chioasma were treated with demacular cosmetics or drugs and quantified by the system. The parameters of treatment groups greatly declined as time went by. the parameters of the drug group declined significantly more than those of the control group (P<0.05).The objective unit-the value of ID was put forward. Conclusion: the image analysis system was proved to be a kind of high potential quantitative means to deal with skin surface pigment. It is harm less to measured skin lesions with high sensitivity, good objectivity and repeativity. The great satisfied clinical effects were reached.