Abstract: The deformation control of subgrade plays a key role in ensuring the smoothness of the railway. The deformation of subgrade is dependent on the traffic loads and the dynamic behavior of subgrade fill materials. A series of drained cyclic triaxial tests are employed to study the dynamic and dissipated energy behaviors of saturated red mudstone fill materials (SRMF), with particular emphasis on the effects of confining pressure and cyclic stress. The results indicate that the permanent axial strain, axial strain rate and equivalent Young's modulus are interrelated via the corresponding state boundary surface (SBS). The variation of confining pressure will lead to change in the shape and size of the SBS. The position of dynamic response in the SBS is dependent on the magnitude of cyclic stress. The two-stage dissipated energy behavior is observed. The dissipated energy is first reduced (stage 1) and then reaches its stable state (stage 2) with loading cycles. The permanent axial strain, axial strain rate and equivalent Young's modulus are strongly correlated with the dissipated energy, and is also portrayed by their SBS. The amount of the dissipated energy in the SRMF corresponds to the cyclic stress level. When the relative dissipated energy level is less than 20%, the SRMF is said to reach the dynamic stable state. When the relative dissipated energy is between 20% and 60%, the SRMF is named as the dynamically critical state. On the other hand, when the relative dissipated energy is greater than 60%, the long-term stability cannot be finally obtained, and the SRMF goes to the dynamically unstable state.