The delay-and-sum structural damage imaging method based on Lamb wave has the advantages of accurate result and low computation cost. However， in complex aeronautical structures， Lamb waves are very prone to reflections because of the complexity of boundary conditions， especially in case of multiple damages. Due to the Lamb wave dispersion effect， multiple wave packets are aliased to affect the positioning results. In response to these problems， this paper proposes a separation and compensation method for dispersion wave packet. Firstly， the aliasing wave packet function considering dispersion effect is theoretically obtained， and the method for solving the sum function is proposed based on hidden variables. Then numerical simulations are used to verify the effectiveness of the algorithm for wave packet separation and reconstruction. Finally， the damage localization experiment of the composite stiffened panel is carried out to demonstrate the capacity of the proposed method. Experimental results prove that it can remove the pseudo-damage projection of the reflected wave under complex boundary conditions， thus improving the accuracy of the damage positioning and the resolution of the image.