Abstract: In order to adopt lens ducts in a coupling system for laser diode array(LDA), the function of the coupling efficiency with the parameters of the lens duct, such as the radius of curvature, the length of the lens duct, the side length of the output face and the fast axis divergence angle was obtained based on mirror-image method. The coupling efficiency of different size of LDA coupling into the laser rod was analyzed. The results are important in designing lens duct for LDA.