The invention relates to a plasticization and injection separated type nested injection machine, which comprises a feeding device, a plunger, a screw, a machine barrel, an injection machine head, a transmission device, a mould, a mould opening-closing device, and the like. The machine barrel is provided with the nested screw and plunger, wherein the screw is outside and the plunger is inside; or the screw is inside, and the plunger is outside. The screw is used for plasticizing materials, and the plunger is used for injecting the materials. The plasticization and injection separated type nested injection machine separates the plasticization and the injection of the materials, and the two operations are finished in the same machine barrel; compared with the traditional reciprocating screw injection machine, the plasticization and injection separated type nested injection machine has high material plasticizing effect; and compared with a two-step injection machine, the plasticization and injection separated type nested injection machine has small equipment volume and short material process.