It is well known that the laser beam can be absorbed and/or scattered during its path from laser head to workpiece surface in laser-arc hybrid welding. It is believed that absorption is generated mainly by inverse Bremsstrahlung in arc plasma of laser-arc hybrid welding, while scattering is governed by Rayleigh scattering in the metal vapour region, formed by laser high-power irradiation on metallic surface. A particle-based numerical simulation technique for these kinds of laser-matter interaction is introduced to predict the redistribution of the incident laser beam energy. The methodology for laser scattering is adopted from the photon mapping technique which is widely used in the rendering process of computer graphics in recent years. The shape of the keyhole in high-power welding is also considered to observe the effect of multiple laser beam reflections in the keyhole.