The non-destructive testing based on Lamb waves has become one of the important means of damage detection of platelike structures. However, the multimode and dispersion characteristics of Lamb waves make them have great complexity in propagation, reception and signal processing. The ultrasonic Lamb waves were applied to study the linear phased array damage detecting. By using the frequency tuning theory, an S0 mode with low frequency dispersion was obtained. The intuitive imaging and precise positioning of the cracked groove damage in the plate structures can realized. The simulation and experiment results showed that the frequency tuning method could be used to optimize the S0 mode with weak dispersion for damage detection, and combining with the linear phased array, the type and orientation of damage could be determined, the effective damage detection information could be obtained as well.