Abstract: The study on the inverse problems in the ultrasonic nondestructive testing (NDT) has a wide application field in various industries. In this paper, an error function based inversion algorithm is introduced to determine the parameters of three-layered plates from the measured velocity of multi-mode Lamb waves. A mixed-spectral estimation is proposed to combine with FFT and AR model for exact detection of the ultrasonic phase velocity. Experiments are performed using two conventional angle probes as transmitter and receiver on the same surface of three-layered laminates. Inverse analyses of one parameter (thickness) and two parameters (longitudinal and transverse wave velocities in a layer, or thickness of two layers) of three-layered laminates are made. The experimental results show that the inverse approach is in good agreement with the actual value.