Abstract： A full-wavefield imaging detection system integrates the point-source/point-receiver scheme with the multi-directional imaging technique. It is equipped with an impacting hammer, a series of three-component velocity transducers and a signal capturing unit. To evaluate the feasibility of this system for detecting defect of high speed railway under-track structure, a full-scaled highway embankment model test with pre-setting defection was conducted and a 3-D numerical simulation using FEM was performed for comparison and mechanism study. The results are in agreement with the numerical ones on the processed scanning images. It is concluded that the full-wavefield imaging detection method exhibits high potential in inspecting the defects of high speed railway under-track structure by imaging.