Active Lamb wave structural health monitoring technology may be influenced easily by the complicated propagation characteristics of Lamb wave in the application. Lamb waves collected have low signal to noise ratio. Research works are carried out to resolve it. Analysis of the direction filter method is proposed in this paper, including the basic principle and implementation method. This method achieves coherent focusing on the useful signal by using the coherence between sensed signals of linear piezoelectric sensor array, monitors and images the damage. At the same time, it can scan the interested direction of the structure. The principle of the direction filter is analyzed. The implementation of the method for the discrete piezoelectric sensor is given. This direction filter method is verified by experiment. In the experimental research on carbon fiber enforced structure, the results show that the method can effectively achieve the focusing and enhancing on damage scattering signal, image and highlight the position and location of damage, and improve signal to noise ratio.