Abstract: Based on the time reversal theory，the active Lamb wave damage imaging method for composite structural delamination detection was researched. The theory basis of the time reversal process was analyzed，and the focusing process to the source was discussed. Depending on the character of Lamb wave propagation，the damage scattering signals were time reversed and reemitted to the damage，and then they will arrive at the damage synchronously so that the damage scattering signal caught again will be amplified. Details about the time reversal amplifying process were analyzed and given. Based on the focalization ability of time reversal theory to the wave origin，the wave propagation was rebuilt by an image method which displays the damage as the focusing point. Experiments on the glass fiber reinforced composite board indicate that the sensing data energy can be amplified by this method，and the location and range of the damage can be expressed well.