With the high speeds and loading, it accelerates the change of structure state and performance of line, and increase disease of subgrade. With the Concealment, complexity and progressive, many problems threaten to safety of train highspeed operation, are not easily detected, and increase the difficulty for maintenance and repair work. In the term of the speed of detection and maneuverability, Traditional means of inspection can not meet the requirements. In this paper, the multi-channel high-speed vehicle GPR system has been used, with speed of 100km / h and 10cm distance of scans. Both diseases, track bed pollution of ballast, deformation of basis bed, and the aquifer situation of base bed can be detected and evaluated. The results showed that: Vehicle GPR can detect the disease, evaluate the status of subgrade of a high-speed railway, at the same time, it can eliminate potential safety hazard, protect the safe operation of trains, to provide a scientific basis for maintenance.