By　using　experimental　results,　the　upper　and　lower　limits　of　the　nonlinear　curves　of　the　dynamic　shear　modulus　ratio　and　damping　ratio　for　conventional　soils　under　different　probabilities　are　investigated.　The　method　and　formula　for　calculating　the　probabilistic　zones　of　the　two　dynamic　parameters　for　the　cohesive　and　cohesionless　soils　under　the　typical　shear　strains　are　presented.　The　approach　is　that　the　experimental　results　are　ordered　by　the　standard　way,　and　the　distribution　form　of　variability　of　two　dynamic　parameters　is　obtained　by　the　frequency　distribution　diagram,　the　tests　of　normality　diagram　and　the　SAS　software.　According　to　different　distribution　forms,　the　probabilities　of　the　upper　and　lower　limits　of　the　two　parameters　under　typical　shear　strains　are　calculated.　The　results　indicate　that　the　relation　between　the　upper　and　lower　limits　of　the　two　dynamic　parameters　and　their　probabilities　can　be　described　by　the　Boltzmann　equation,　in　which　the　parameters　depend　on　the　soil　type　and　the　shear　strain.　For　all　probabilities,　the　ranges　of　the　shear　modulus　ratio　for　different　shear　stains　are　obviously　different　while　the　most　ones　appear　at　10-4-10-3　of　the　shear　strain.　For　the　same　probability,　the　range　of　the　damping　ratio　increases　with　increasing　shear　strain.　The　proposed　formula　for　calculating　the　probabilistic　zones　of　the　two　dynamic　parameters　lays　a　foundation　for　the　reliability　theory　in　soil　dynamics　and　earthquake　engineering　to　some　extent;　and　it　also　can　directly　supply　the　technical　support　to　the　risk　evaluation　of　a　seismic　design　and　seismic　safety　of　engineering　structures.