Abstract: There is a higher requirement of post-construction settlement and long-term dynamic stability for the high-speed railway subgrade. In order to satisfy this requirement and provide reference for the selection of subgrade fillers in loess areas, this paper uses the short-term and fatigue dynamic triaxial tests to examine the change in the dynamic stability evaluation parameters (short-term and fatigue dynamic shear strain threshold) (SDSST and FDSST) of the cement-improved loess with cement content (η), confining pressure (σ3) and consolidation ratio (Kc). The relationship between SDSST and FDSST is discussed, and it is expected to obtain the fatigue dynamic shear strain threshold by the convenient and rapid short-time dynamic triaxial experiment. The results show that (1) under the short time conditions, the vertical plastic strain increases with the increasing dynamic stress, and finally presents the characteristics of brittle failure, while gradually decreases with the increase of η, σ3 and Kc. (2) The dynamic modulus Ed increases first and then decreases with the increasing dynamic stress σd, while Ed shows a positive correlation with the increase of η, σ3 and Kc. (3) The SDSST and FDSST, and the dynamic stress threshold linearly increase with the increase of η, σ3 and Kc. (4) Under the same condition, the ratio of FDSST to SDSST of the cement-improved loess ranges between 0.29 and 0.34, which changes little with the increase of η, σ3 and Kc.