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.