Abstract: Numerical simulation is made of the liquid-solid multiphase flow system in the shallow-bath heavy medium separator using the software ANSYS FLUENT. After introduction of the 150~6 mm particles into the separator, the trajectory of the motion of the particles in the bath is investigated with the use of the coupled discrete-phase model. Through measurement of the different displacements of particles in the X-direction and the Y-direction when the medium suspension varies inupward flow velocity, the relationship between the separator′s lower size limit of separation and the medium suspension upward flow velocity is derived.