Abstract: The device which can simulate the thermal ablation in a solid rocket motor was used to make the sample of charring layer of Ethylene-Propylene-Diene Monomer (EPDM) heat-insulating material. The structure characteristics of charring layer were analyzed. A suit of device used for researching particle eroding charring layer of heat-insulating material was designed. It is carried out three tests of particle eroding EPDM charring layer with the erosion angles of 30°, 60° and 90°, respectively. The process of erosion is recorded by high-speed camera. The velocity of eroding particle is gained by analyzing the image. The force particle acting on the charring layer is computed by the law of momentum. The limiting shearing and crushing stress is derived by comparing the testing data, which can be applied to the model ablation of EPAM under considering the eroding effect of gas and particle.