Research methods: In the past the subgrade can be damaged by the old measuring method and the real situation of it can not be discovered fully. Now combined with the fact situation，the none-damaged measuring method is accepted to research the subgrade totally ， so that the stability of subgrade is evaluated.
Research results: By testing some proper physical volume，the present manner and disease of the existing railway subgrade is well detected，relating with the standard value of regulation. And evaluation of the subgrade stability is also provided.
Research Conclusions: This paper presents how to use the geological radar and transient Rayleigh wave method to test the existing railway subgrade，and summarizes a complete testing method that is of high maneuverability，rapid， accurate，simple and convenient ， none-damaged and effective. By determining some physical quantities and analyzing the relativity between the physical quantities and the values in specification，this method can accurately disclose the status quo and disease of subgrade and evaluate the stability of the existing railway subgrade. It is very important for traveling safety and has remarkable economic and social benefits
2007, Vol. 24 
