The dynamic apparent viscosity of polymer melts during pulsatile extruding flow with a vibration force field was studied on a self-made dynamic capillary rheometer (DCR). A theory that could reflect the vibration influence on the dynamic apparent viscosity was proposed. Due to the superposition of the vibration force field upon the steady shear flow, the phase difference between the shear stress and the shear rate could be chosen as a parameter to reflect the effect of vibration on the dynamic apparent viscosity. According to this theory, the average shear rate during pulsatile extrusion increased because of the existence of the phase difference, which caused the decrease of the dynamic apparent viscosity. The experimental results proved that the phase difference was reduced with the increase of vibration frequency, which resulted in a decrease in the dynamic apparent viscosity during the pulsatile extrusion.