Numerical modeling was performed for ablation processing of a solid particle in a thermal plasma flow. The model is based on Constrained Interpolation Propagation–Combined and Unified Procedure (CIP–CUP) method, which can simulate incompressible and compressible flows and then the multiphase flow. Furthermore, the volume of fraction (VOF) function was introduced to track the surface of the solid during ablation. Using that developed model, the ablation process of a polyethylene particle was simulated in a thermal plasma flow. Results show that ablation occurs more strongly at the particle's upstream surface, thereby producing strong gas flow. © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.