In order to obtain the deformation characteristics a foamed mixture lightweight soil using river sludge(FMLSS)under a dynamic load, the effects of the confining pressure, water content, cement content, and air foam content on the dynamic deformation characteristics of the FMLSS were investigated using laboratory dynamic triaxial tests. Test results show that the fitting dynamic stress-strain curve of the FMLSS is of the hyperbolic type. The dynamic strain of the FMLSS decreases with the increase of confining pressure and cement content, and increases with the increase of water content and air foam content under a certain dynamic stress lerel. Under a constant dynamic strain, the dynamic elastic modulus of the FMLSS increases with the increase of confining pressure and cement content, and decreases with the increase of water content and air foam content. The relationship curve of the dynamic elastic modulus and dynamic strain shows a gradually decreasing trend. The water content and air foam content are the main factors influencing the dynamic deformation characteristics of a FMLSS.