It's known to all that the GPR can be used to detect the road surface vacancy. Nevertheless, the detection of the exact

height of the road surface vacancy remains an unsolved problem. With the financial support by the Guangdong Geological Funds, the

authors established the models for the road surface vacancy in accordance with the road structure and made tests. It is concluded

that there exist positive correction between the amplitude of the GPR reflection and the height of the road surface vacancy. The

formula for determining the height of the road surface vacancy by the Ground Penetrating Radar was thus established. This means is

very practical because with the formula the detection of the road surface vacancy by the Ground Penetrating Radar becomes very fast

and the precision can be ensured.