Abstract: Based on the dynamic triaxial tests on disturbed unsaturated samples, a study on the dynamic characteristics of modified fly ash loess is carried out. The dynamic stress-strain relationship of fly ash loess under loading function is discussed. The influence of adding amount of fly ash on the dynamic constitutive relationship, dynamic modulus of elasticity and damping ratio of the modified loess is analyzed. The results show that the dynamic constitutive relationship of the modified loess with different adding amounts of fly ash obeys the hyperbolic equation. The test constants aand bdecrease with the increase of the adding amount of fly ash. The dynamic modulus of elasticity increases with the increase of fly ash amount, but the damping ratio noticeably reduces. The optimal content of fly ash of the fly ash-modified loess is 15%~20%.