Abstract: The structure and the performance of the injection part of the hydraulic vibration injection molding machine are presented. The axial force distribution of the screw is analyzed. By simplifying the actual screw to a generalized model, the physical model and mathematic model to describe the screw’s axial vibration in the injection process are established using the method of lumped-mass, and then the screw’s dynamic responses are examined. Results show that the vibration amplitude of the screw decreases with the increase of frequency; and the amplified coefficient of amplitude in low frequency is bigger than that in high frequency in the range of adjusting frequency. The experimental results are in good agreements with those of theoritcal analysis.