The phased array beam steering is controlled and the Lamb wave phased array theory is discussed in detail.Phased array technology is used to control the time delay of the Lamb wave and to make the Lamb wave focus on the structure damage.The damage scattered signal is extracted by comparing the health signal and the damage signal.The Lamb wave signal direction is controlled by utilizing the time delay to the excitation signals and the damage scattered signals and the structure is monitored in all orientations.The processed signals are shown on the mapped image in gray-scale.The gray-scale in the mapped image from dark to light corresponds to the amplitude from low to high.The location where the max amplitude of the signals lie is the damage location in the structure.Finally,the proposed method is verified by an experiment on aluminum sheet structure and the result shows that it is effective to identify the damage position of structure and to display the damage clearly.