In order to reduce the number of metal fragment produced by non lethal ammunition explosion, the cast structure of metal extension tube was designed. Based on the burning characteristics of the ignition composition and the structural action principle, the stripping process was analyzed and the stripping trajectory model was established. The change laws of the gas pressure and the velocity of the extension tube were obtained, and the model was verified by high speed photography. The results showed that the error between the maximum speed and the actual speed was only 0.5 m/s. It was proved that the mathematical model was reasonable and it provided theoretical guidance for the design and optimization of the structure of the extension tube stripping.