When processing of the laser cutting, welding, punching or marking, the incidence laser beam on a surface of materials has a very high energy density. Laser beams on the surface of materials is reflected by the reflection of materials or absorbed by exponential decaying rate of light intensity. At the time, Laser beams can change to heat energy and increase the material temperature. From this phenomenon, We obtain the high temperature near a laser spot and laser processing is possible. The reflection rate on a surface of materials is a important quantity to decide the laser processing. - Reflection rate is various according to the wavelength of laser light, material types, surface state. - Generally the reflection rate of a metal is higher than the ceramic, plastic, and trees. Absorption coefficient decides how fast the laser energy decays at the penetration of a material. (Absorption coefficient) 1 / wavelength ¡á From this formula, a ultraviolet light has a high absorption rate and a infrared light has a low absorption rate. ¡á The temperature of a surface is very fast increasing on the material of the high absorption coefficient - From this formula, we can define the penetration depth, Penetration depth = 1 / absorption coefficient ¡á Penetration depth of a laser light on a surface of materials ¡á Laser processing is only possible within the penetration depth.