Abstract: Taking the soil density and water content into account,a numerical model of moisture migration in unsaturated loess subgrade was given,and parameters of the model were obtained.It was put forward that the coefficient of water volume change m2w was not only related to moisture content,but also to soil density.The change of m 2w resulted from density change was large in loess with more moisture content,and is was small in that with less moisture content.Coefficient of permeability kw was also related to the loess density.Based on analysis of nonlinear relationship between kw,m 2w and water potential,time interval was got.Furthermore,by simulating unfavorable rainfall,moisture migration in loess subgrade was studied.The slaking scope in subgrade by seepage was gradually enlarged.The slaked area was related to the loess density,small density of subgrade loess resulted in large slaking scope.Eonstructing subgrade in loess with large density was advantageous to avoid seepage damage.