In order to study the structural dynamic response and the separation rule of launch tube and missile of the overhang cold launching system during launching, and provide a basis for the design of new overhang launching system, a dynamic model of the overhang cold launching system was established by using the rigid-flexible coupling method and multi-body dynamics according to the structural characteristics and ejection physical process of the overhang cold launching system. The accuracy and rationality of the modeling method proposed by this paper were validated against the test. Based on this, the dynamic response of ejection and outlet attitude were analysed. The results show that the dynamic model of overhang cold launching system can accurately reflect the vibration characteristics of the system. A large longitudinal displacement of the center of launch tube will occur during the ejection process. The oscillation frequency is relatively small, but the structural vibration caused by the ejection impact will have a great influence on the pitching attitude of the missile. The vibration response of the adjacent launch tube is small, which is beneficial for the continuous launching of the overhang launching system. The research results can provide a basis for the subsequent design of vibration reduction.