Phase delay mirrors were designed and prepared to regulate femtosecond laser systems’ group-delay dispersion (GDD). This paper systematically investigates the principle of compensating group-delay dispersion by phase-delay mirrors. Nb₂O₅ and SiO₂ were used as the materials with high and low refractive indices. The group-delay dispersion curves were smoothed out by pairing the phase-delay mirrors with their complementary mirrors. The phase-delayed mirrors with phase modulation data of -800 GDD were prepared, and the reflectivity reached more than 99% in the range of 900 nm-1100 nm. The bandwidth adjustment problem of femtosecond laser systems is solved to meet the requirements of femtosecond lasers