The divergence angle of an incident beam will change the characteristics of a narrow-band angle-tuned thin-film filter whose passband will decrease and divergence loss will increase. This phenomena will be more and more obvious while the incident angle is increasing. Here its reason is analyzed. According to the Lagrange-Helmholtz principle, a beam expander is designed to compress the divergence angle of the incident beam. The double filtering technology is used to enhance the passband stability and the rectangle factor of the angle-tuned filter. One kind of shaping optic system is fabricated to the 100 GHz DWDM narrow-band angle-tuned filter. Experimental results show that the shaping system could effectively eliminate the influence of the divergence angle to the filter.