Based　on　the　plastic　flow　theory　of　soils,　an　elastoplastic　constitutive　model　for　describing　the　dynamic　response　behavior　of　the　saturated　sands　is　developed.　The　total　deformation　of　soils　consists　of　three　parts:　elastic　strain,　the　plastic　strain　related　to　the　volumetric　yielding　mechanism　and　the　plastic　strain　related　to　the　shear　yielding　mechanism.　The　difference　of　soils　behavior　in　virgin　loading　contrast　to　unloading　and　reloading　can　be　reflected　by　adopting　different　model　parameters.　By　comparing　the　results　calculated　by　the　model　with　the　test　data,　it　is　shown　that　the　presented　constitutive　model　can　describe　the　response　behavior　of　saturated　sands　subjected　to　cyclic　loading　with　reasonable　accuracy.　The　number　of　the　model　parameters　is　limited　and　their　value　can　be　calibrated　through　conventional　triaxial　compression　test　and　hydrostatic　pressure　test.　In　the　meantime,　the　form　of　the　constitutive　model　is　simple　and　it　is　suitable　for　numerical　calculation.