The effects of the motion of atoms or molecules on the dissociation probability of the H2-Pt(111) system were analyzed by molecular dynamics. The embedded atom method (EAM) was used to model the interaction between a Pt(111) surface and an H2 molecule to consider the dependence of electron density. Initially, the EAM potential was constructed to express the characteristics of the system, such as the electron density or dissociation barrier at certain sites and orientations, as obtained by density functional theory (DFT). Using this potential, simulations of an H2 molecule impinging on a Pt(111) surface were performed, and the characteristics of the collision were observed. These simulations were performed many times, changing the orientation of the H2 molecule, and a dynamic dissociation probability at each site against impinging energy was obtained. On the other hand, a static dissociation probability was defined from the dissociation barrier of a hydrogen molecule obtained by the EAM potential. These results were compared to one another, and the effects of the motion of atoms or molecules, which were called dynamic effects, on the dissociation probability were analyzed. The dynamic effects on the dissociation phenomena were very large at the top site, but were small at bridge or fcc sites.