Research conclusions: Based on the systematic analysis and research，the heat stability ， ice content ， distribution of unfavourable frozen soil and its change regularity of the permafrost region in which the railway line crosses are found out which can provide basic guarantee for tackling difficult problems of construction of railway in permafrost region. The design idea and treatment principle of“lowering temperature actively，cooling subgrade and protection of frozen soil" are presented to the subgrade engineering，and the concrete type of engineering structure is also offered.