The experimental results show that (1) light reflection occurs not only from the skin surface, but also from tissue layers below the the skin; (2) between 400-800 mn, the absorption peak of reflectance curve of tha human body is at the same wavelength as that of the transmittance curve of the blood; (3) between 400-800nm, the reflectance and transmittance curve of the skin or that of the skin plus subcutaneous tissues have essentially the same changing tendency.