Abstract: The multiple modes and dispersion nature of ultrasonic lamb wave as well as the anisotropies of composite material limit composite material application and research. Taking the glass fiber plate as case study, the paper put forward a graphics method to dispose dispersion equations for plotting the dispersion curve, analyzing the dispersion nature and calculating the velocity of A0 and S0. Based on it, an experim ental test system is set up, the characteristics and velocity of sensor signals are extracted using HHT, according to the calculated value of A0 and S0, the single mode of lamb wave is achieved，which can be used for detecting composite material widely.