According to the filed frost damage investigation,frost heaving test and moisture migration simulation test,this paper describes results from filed and experimental data that investigated the reason and factors affecting freeway subgrade frost damage in seasonally frozen ground region.The results of field observation and the test series are compared to discuss the relationship of frost damage and water content,the origin of water on frost damage,the characteristic of water translocation and the road frost boiling caused by the lime-ash-soil deterioration of the subbase.Furthermore,by virtue of comprehensive study of this project,the distribution data of capillary water along the height by standpipe method are combined with the change law of frost heaving radio and water content,then the effective frost damage height can be obtained.Experimental results show that the values in specification are lower than those in test in some cases,which is unfavorable for the design of the subgrade prevention frostbite and anti-freeze.These results are significant for the design of the least height of road embankment and the depth of prevention frostbite at the site of excavation.