Abstract: On the base of un-drained dynamic tri-axial shearing tests. It examines the five influence factors on the dynamic properties of saturated loess, where the loess has its original internal structure. The five factors are the initial consolidated pressure, the over-consolidation ratio, the consolidated ratio, the dynamic shearing stress ratio and the frequency. The results are compared to other references and analyzed in detail. The structure of saturated loess is emphasized. The destroy of the loess's internal structure is a turning point for the dynamic properties. It is reasonable to use plastic strain to describe the change of structure and constitute the supper-pore pressure model. The relevant formulation is also given.