Abstract: As a method of assessing diffusing defects in materials and the variety of mechanical properties, acousto-ultrasonic techniques have been successfully used in the NDT of the composites, bonding and lumber. This paper provides an overview of the acousto-ultrasonic techniques. Based on the principle of the technique, the implementation and the influence factors were discussed. A few emphasis aspects included the natural modes and dispersion modes in academic analysis, stress wave factors, ultrasonic decay rate and the statistic analysis. In the end a conclusion and some challenging issues were proposed.