Research conclusions:The study shows the natural loess isnotsuitable forbeing the filling ofroadbed directly due to its the big porosity, water sensitivity and collapsibility for the ballastless track requiring less settlemen,t so the natural loess mustbe improved. After improvemen,t its coefficientofcompression is loweredmuch, its strength andwater stability of loess are highly improved, and its collapsibility is removed. The improved loess can be as highly qualified filling materials forhigh-speed ballastless track when the construction quality is guaranteed in mixture ratio, water conten,tlaying thickness and compactness.