We have been studying in dynamical behaviors of hydrogen on the GaAs(001) surface using a supersonic molecular beam apparatus. We measured the angular and time of flight distributions of reflected beams, when hydrogen molecules were injected at [110] and [(1) over bar 10] directions onto the GaAs(001) 2x4 surface. A comparison of measurement and classical trajectory simulation showed that angular distribution consisted of inelastic direct scattering and complicated multiple scattering on the GaAs(001) 2x4 surface with large surface corrugation. The depth of the potential well of hydrogen molecules on the GaAs(001) 2x4 surface was estimated to be 0.4 kcal/mol, indicating the importance of information on energy exchange from translational to rotational modes.