The instantaneous degradation of erosion surface of ethylene propylene diene monomer (EPDM) insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography system.The images of its erosion state and dynamic ablation rate were obtained. And the charring-layer was analyzed by using SEM and energy spectrum. The experimental results indicate that the erosion rate of EPDM insulation layer impacted by low speed and low concentration particle flow is relatively small in the 1 st second since the motor starting, but increases rapidly in 1 to 2.5 s, while the erosion rate of EPDM insulation layer impacted by high speed and high concentration particle flow increases rapidly in the 1 st second; the ablation rate at the section eroded intensively by particle flow increases at first, then decreases, and goes to stabilization after 4.5 s; the higher speed and concentration particle flow are, the deeper particles get into charring layer, which lead to more thermal increment and thinner charring layer.