Frequently, ferromagnetic and nonmagnetic particles are included in the delivery fluid when the vertical mixed flow pump with magnetic bearings works. As the magnetic attraction, the magnetic particles are easily adsorbed to the magnetic bearing gap and united with the nonmagnetic particles into a group, causing the magnetic bearing wear. To tackle this issue, magnetic separator device was installed in the existing bearing structure according to the flow field near the magnetic bearing work space. The mathematical model of the separator was created by multifield coupling way. The distribution and movement of particle phase around the separator and magnetic bearings work space were studied by numerical simulation. The results show that:the ferromagnetic and nonmagnetic particles which are away from the magnetic bearing clearance are flowed and transported to the pump outlet; the ferromagnetic particles are attracted around magnetic bearing operating clearance and coagulated into a group with nonmagnetic particles; with increase of adsorption grain groups, part of the grain groups gradually fall off and are taken away by fluid as the magnetic force of external grain groups is small; the situation occurs periodically. In addition, the group of adsorbed particles around the magnetic bearing gap plays a role to prevent followup particles into the magnetic bearing work clearance.