Using a simulation of physical model and according to the analogical principle,a simplified double-layer model of the surface and roadbed of concrete highway is established,practical methods of distinguishing the reflected ultrasonic wave,measuring the velocity of the reflected ultrasonic wave and the time parameter,which the ultrasonic wave takes from leaving source to the received by receiver,are put forward.With a special observation system,the surface thickness of concrete highway is derived by the velocity and time parameter.It is shown that the result is high precise with a relative error less than 3% and this non-damaging inspection can be applied to other area.