The plunger injection molding machine pushes forward the fused plastics in the charging barrelthrough the to-and-fro movement of plunger therein, and the spreader further injects them into the mold cavity through the nozzle. The plastication of plastics in the charging barrel mainly depends on the heat provided by the outer heater of charging barrel. The poor thermal conductivity of plastics results in the unbalanced plastication to the inner and outer layer of materials in the charging barrel and therefore, the plunger injection molding machine is not suitable for the molding of plastic parts with low fluidity, strong heat sensitivity and overlarge amount of injection.