The object of the present invention is to provide a polyolefin polymerization method which prevents fine particles of polymer from scattering from a fluidized bed in a gas phase polymerization reactor. This object is achieved by a process for polymerization of α-olefin in multi-stage polymerization process and in at least two serially arranged polymerization reactors including a gas phase polymerization reactor, the process comprising; drawing out polyolefin particles from a polymerization reactor, and transferring the polyolefin particles into the interior of fluidized bed of a gas phase polymerization reactor of the next stage.