This work includes the numerical study regarding the spatial ratio of the radiation force and drag force in the channel for acoustophoresis based on the standing surface acoustic wave (SSAW). Although several numerical studies found that both pressure and streaming fields are not homogeneous in a channel, the spatial distribution of the radiation force and the streaming one, which can determine the displacement of particles in the channel, have not been examined. In this study, we calculated the ratio of the radiation force to the drag force in a channel in combination with SSAW and investigated how it determined motions of particles as a function of particle size.