Abstract: The effects of impeller installation height and stirring speed on the hydrodynamics and the suspension state of the Mg(OH)₂ particles in large scale reaction crystallizer were studied by multiple reference frame (MRF) and the standard k-ε model in Fluent software. The simulated results showed that the appropriate increase of impeller installation height was benefit for the settling and discharging of the coarse particles, which mainly attributed to the decrease of flow velocity in the bottom zone of the crystallizer. When the installation height was too high, the flow velocity in the baffle cylinder was increased, which caused the nonuniformity of the flow velocity. The low stirring speed was disadvantageous for the suspension of Mg(OH)₂ particles. With the increasing stirring speed, the nonuniformity of the flow velocity in the settling zone was significantly improved and the particles in the crystallizer were more uniform in suspension state. The optimal installation height of impeller and stirring speed were determined to be 3.3 m and 70 r/min, respectively.