When spacecraft dock with each other, impact will rise at the docking point. It is assumed in this paper that a docking platform having the shape of Stewart platform is attached at the one of the docking spacecraft to reduce the effect of impact. Although the impact between two spacecraft at the contact point of the upper plate of the platform is very large, the impact is absorbed by the docking platform and a negligible impact is transmitted to the spacecraft. To show this, the modeling of the internal impulses at the joints of multibody system is introduced and the internal impulses of the docking platform are analyzed by the modeling method.