The introduction of vibration force field changes the mode of movement and state of polymer melt molecule. The research of the polymer melt molecule movement under the impact of vibration force field can serve as the basis for determining those physical parameters during polymer material processing. To analyze the polymer melt molecule dynamics，a bead-spring model is presented，which can describe the movement process of polymer melt molecule under the impact of vibration force field，and the model is solved by using the statistical mechanics method. In the end，the expression of laxity time and frequency is obtained，which indicates that，laxity time is related to frequency，when other parameters are invariable，laxity time will decrease as frequency increases. The model will serve as the theoretical base for polymer processing and equipment design.