This paper investigated the absorption of a micro-particle irradiated by laser. Micro-particles usually appear within the plasma induced by a laser or powder in the process of laser cladding. These particles are assumed to be spherical and neutral (no surface charge). Laser-particle interactions involve scattering, refraction, and diffraction phenomena. Refraction and diffraction can enhance radiation absorption. The complex optical indexes of material and size parameters of micro-particles characterize the absorption of particles in these materials processing. The electromagnetic wave theory and geometrical optics approach were utilized to analyze the absorption in the particle. The errors between these two methods were discussed for different indexes of absorption and size parameters. The compatibility of geometrical optics approach for a small particle is also presented.