Double-grating coupler based on two fiber-Bragg-gratings (FBGs) has the advantages of compact structure and enhanced filtering efficiency. The influences of gratings′ characteristics were investigated thoroughly, and the result showed that maximum drop efficiency and minimum backreflected return wave could be achieved by choosing proper gratings′ position in the coupler region. Furthermore, by adjusting the gratings′ length and ultraviolet (UV) refractive modulation depth, a novel balanced configuration with the two Bragg gratings inscribed into the coupler waist′s center was designed and fabricated, which showed simultaneously optimized add and drop filtering responses. The experimental measurement demonstrated that the uniformity of coupler waist should be responsible for the inequality in drop bandpass, and the filtering performance of double-gratings coupler can be enhanced by improving fused taper technique.