Ultrasonic nondestructive evaluation (UNDE) of notch defect by Lamb wave is investigated theoretically and experimentally in this paper. It is hard to predict and explain the received Lamb signal of UNDE due to its dispersive nature. The width of the notch is available by delay time between reflection signal and first echo signal, and its depth can be evaluated by reflection coefficient. A model by FEM (finite element method) has been used to predict reflected signals by boundaries of defect and the end of the plate. In comparison with the results from the theory and experiment, it is confirmed that FEM is efficient for predicting lamb wave signal propagation and interaction with defect in plate for UNDE.