Research conclusions: Based on the on － site investigation and the composition of subgrade filling of the existing railway，it is necessary to evaluate the subgrade of the existing railway section by section to reduces the negative influence caused by discrete data and improve the accuracy of the valuation results． The defect locations of existing Baicheng － Aershan Railway in bearing capacity and strength mainly concentrate in the range of 0． 0 ～ 0． 6 m of the road base＇s surface and 0． 6 ～ 1． 2 m range of the bottom． The deep filling should be conducted to them in a big range for more test and evaluation． The dynamic penetration test has features of simple operation and wide applicability，but itstest data is of big discreteness and how to reduce the error is the problem to be resolved in future． Compared with the Evd ，the K30 requires a lot of human and material resources and much time ． The comparative experiment can be done to the existing railways of different grade with these two methods to explores the relation between Evd and K30，and substituting Evd for K30 partially in the test points can improve the work efficiency． The defect position and scope of railway road base in the bearing capacity and strength can be accurately revealled by using the spectral analysis of surface waves along with the dynamic penetration test to evaluate the condition of the existing road base．