Considering the interaction between the piezoelectric transducer (PZT) and the plate, a frequency adjusting method of generating single mode Lamb waves using single piezoelectric transducer is presented in theory. The application of mode selection in Lamb wave structural health monitoring is experimentally given. The theory has the ability to predict the amplitude of each Lamb wave mode as a function of frequency for given plate material and thickness, and specific PZT size. Optimal actuating frequency can be identified at which the wave amplitude for a particular mode is maximized while the wave amplitudes for other modes are relatively minimized. Numerical results are presented to validate the theory and show the capability of single mode Lamb wave selection. Different frequencies that correspond to a preferential A0 mode, a preferential S0 mode, and both the A0 and the S0 modes are excited for damage imaging, respectively. The results show that the single Lamb wave mode detection can locate the damage more accurately, demonstrating the importance of the mode selection in Lamb wave structural health monitoring.