The vertical take-off event of launch vehicle was divided into static phase, hold-down phase and release phase, and the computational result fields of the previous phase provided the initial condition fields of the next phase. A new analysis method to compute the launch vehicle's structure transient response during the hold-down and release phase was proposed in this paper, using the field transferring function and group analysis function of the MSC.Patran/Nastran software. This analysis method solved the difficulty brought about by the changed boundary condition (the separate face between the launch vehicle and the launch pad) during the structure transient response computation course. Several examples of launch vehicle's structure transient response during the hold-down and release phase were analyzed by the proposed method. The variety characteristics of hold-down force during hold-down phase and the vehicle's structure transient response during the release phase were obtained. The computational results indicated that the analysis method is both simple and convenient, and the computational result was quite accurate. The method can be used to make efficient analysis of the influence of the different release time, the disappearing characteristics of the hold-down force, the dispersion of the release time, the restrain force of soft release mechanism to the vehicle's structure transient response. It can provide reference for the design of the hold-down and release mechanism.