The absorber based on planar metal/dielectric thin films has attracted much attention due to its superior absorption performance, simple preparation process and broad application prospects. In order to improve the absorption performance, an ultra-broadband perfect absorber with a multilayered Zr/SiO₂ structure is proposed, which is based on multiple Fabry-Perot (FP) resonant absorption. The structural parameters are optimized by employing the transfer matrix method combined with the genetic algorithm and the calculation results show that as for an absorber with a 10-layered Zr/SiO₂ structure (which constitutes 4 series FP cavities), the minimum absorption efficiency exceeds 96.6% and the average absorption efficiency is up to 98.6% in the wavelength range of 0.4--3.0 μm. Even as for one with only a 4-layered structure, its average absorption efficiency still reaches 91.5%. Furthermore, the absorption characteristics of the proposed structure are analyzed in other wavelength ranges and the relation of its average absorption efficiency with lay number is also calculated. Compared with other absorbers with complex structures, the proposed absorber has the characteristics of large working bandwidth, high absorption efficiency and simple structure. It has wide application prospects in the fields of solar energy collection, heat radiator, and infrared cloaking.