Abstract: Three-dimensional isothermal material flows in the metering section of injection molder with different screw heads during injection molding are simulated through POLYFLOW software.The velocity fields,pressure fields,viscosity fields and stress tensor fields at different time in the yz section and the xy section are respectively analyzed in detail.It is shown that the velocity gradient and the pressure of the injection screw with the screw thread in the head during injection molding increase along the screw axe.The shear effect is strengthened,and viscosity of the melt polymer decreases.Also the flow of the melt polymer in the screw channel is blocked by the screw thread in the head.Then the velocity gradient decreases,and the stress tensor decreases obviously while the viscosity increases,and the shear effect is weakened.