Abstract: The analytic expression of received echo in multilayer NDT is derived first.From the analytic resolution,interface signals are analyzed.It is concluded that the received ultrasonic echo of multilayer is composed of all theinterface signals.Therefore,the second interface signal can be extracted by the adaptive canceling of the zero and flrstinterface signals.The processing effect to the ultrasonic echoes of simulation and real multilayer is pretty well.From theamplitude and arrival time of the second interface signals,the bond and the depth of the interface can be evaluated.