Abstract: Dynamic triaxial tests were conducted on Xi’an intact loess with different water contents and disturbed saturated loess with the same dry density as intact loess.A quantitative comprehensive structural parameter mε d was defined using ratio of secant modulus Edy of intact loess and secant modulus Edrs of disturbed saturated loess under dynamic triaxial stress condition,which could not only reflect arrangement but also coherent structure of soil particles.The effects of water content and consolidation confining pressure on the structural parameter were investigated under cyclic loading.It was indicated: ① The structural parameter could not only reveal the influences of water content and consolidation confining pressure on structure of intact loess under dynamic triaxial stress but also was rational and sensitiv as well as stable.The characteristics of dynamic stress strain could be rationally explained with that the structural parameter decerased with the increase of water content and consolidation confining pressure.② The relationship between quantitative variation of the structural parameter mεd0? mε and dynamic strainε d could be fitted with hyperbola(mε d0 was the initial structural parameter),and the equation of the structural parameter obtained could reveal the influence of consolidation confining pressure,water content,density,dynamic stress and dynamic strain on structure of the intact loess.③ A constitutive relation describing dynamic stress-strain behaviour of intact loess was presented by introducing the structural parameter to equivalent linear model of disturbed saturated loess,which could consider moistening and cyclic loading effect on structure of intact loess.Its rationality was confirmed by the agreement between the calculated and test results.