Abstract: To excite single S₀ mode and single A₀ mode of Lamb waves,two same piezoelectric ceramic wafers of which diameter is 14 mm and thickness is 0.8 mm bonded in the PMMA plate symmetrically are applied as actuators,and a piezoelectric ceramic wafer of the same size arranged in another position is applied as the sensor.In the frequency range of below 100 kHz,according to pitch-catch arrangement,the actuator excites Lamb waves alone or two actuators excite Lamb waves in parallel symmetrically or antisymmetrically.And then the change of mode components in the signals received by the sensor is analyzed.Based on the experimental result,three Lamb wave excitation methods are applied to detect the simulated defect in the plate.Experimental results show that in a certain frequency range,the method of exciting piezoelectric ceramic wafers in parallel symmetrically can suppress A₀ mode effectively,and acquire single S₀ mode relatively,and meanwhile the method of exciting piezoelectric ceramic wafers in parallel antisymmetrically can suppress S₀ mode effectively and acquire single A₀ mode relatively.The fewer the modes of Lamb waves excited are,the easier it is to identify the echoes from the defects.