Stable structure of subgrade of railway is an important foundation for safety of train. Rising of speed and heavy transport tasks accelerate deterioration of ballast and increase disease of subgrade. It is more important how to detect and maintain the condition of ballast and subgrade highly effective, faster and without any destruct. In recent years, the ground penetrating radar has been an effective method for detecting and evaluation ballast and subgrade. This paper present application of detecting and evaluation ballast and subgrade by using the train-mounted-multicenter ground penetrating radar(GPR), data processing and interpretation, acknowledge and some problem.