The dynamic laser speckle from a skin surface provides the information about blood flow in the capillaries.The temporal fluctuation of the speckle is not only dependent on the red cells movement and illuminating condition,but also the thickness of the epidermis,so the determination of the blood flow information will be affected by the variant human skin.In this paper,the influence of epidermis on the evaluating skin blood flow is studied experimentally,and the relationship between the skin thickness and the time auto correlation is presented.