Abstract: The traffic load and the drying-wetting cycle have an important influence on the strength characteristics and stability of fly ash-modified loess subgrade. To illustrate the influences of drying-wetting cycle on the strength of the fly ash-modified loess, a series of dynamic triaxial tests on the fly ash-modified loess samples with different fly ash contents are conducted after different drying-wetting cycles. Based on the test results, the dynamic residual deformation and dynamic strength evolution characteristics of the fly ash-modified loess are analyzed. The influences of fly ash content and drying-wetting cycle on the residual dynamic deformation and dynamic strength of the modified loess are discussed. The optimum proportion of the fly ash-modified loess is proposed. The results show that the fly ash-modified loess can significantly improve the dynamic strength of the subgrade and effectively decrease the dynamic residual deformation of the modified loess. The critical dynamic stress of the modified loess is the largest and the dynamic residual deformation is the smallest when the fly ash content m=30%. After the drying-wetting cycle, the critical dynamic stress of the modified loess decreases whereas the dynamic residual deformation increases. The critical dynamic stress decreases firstly and then increases with the increase of the drying-wetting cycle. However, the decrease rate of the critical dynamic stress decreases with the increase of the drying-wetting cycle. The dynamic residual deformation of the fly ash-modified loess becomes stable after 2 drying-wetting cycles. In addition, the modified loess subgrade has an optimum behavior under the coupling effect between traffic load and drying-wetting cycle when the fly ash content m is between 25% and 30%.