The dynamic characteristics of soil are mainly related to the stress condition, loading type, test control mode, load, and other parameters. Previous experimental study on the cumulative deformation of unsaturated loess under uniaxial dynamic stress loading can not truly reflect the stress state of soil. In this study, the WF-12440 dynamic triaxial-hollow cylinder torsional shear test system produced by WF Company, UK, was used to carry out a series of long-term repeated load tests of loess under unidirectional and bidirectional dynamic stress loads. The effects of different dynamic stress loading methods on the development characteristics of cumulative deformation of unsaturated loess. The test results showed that the softening index of loess decreases non-linearly with the increase of cycle times both under unidirectional and bidirectional loading. At the same cycle times, the softening index decreases with the increase of dynamic stress amplitude. Under different loading modes, the softening index decreases rapidly within 100 cycles, and the softening rate tends to be stable with the increase of cycles. Under the action of bidirectional load, when the axial dynamic load is small, the application of radial load will accelerate the softening degree of loess; with the increase of axial dynamic load, the effect of radial load on soil softening will weaken gradually. With the development of this study, it can be more accurate to evaluate the seismic subsidence of loess field or calculate the deformation of subgrade soil under different load coupling changes in Northwest China, so as to effectively control the overall stability of subgrade and the settlement after construction.