Herein, a mid-infrared absorber based on the hexagonal boron nitride material is designed. The absorber is an one-dimensional grating comprising a truncated pyramid-type unit structure whose absorption mechanism is based on magnetic polaritons and Fabry-Perot cavity resonance effect. The influences of the structural parameters, working wavelength, and incident angle of the absorber on absorption performance are analyzed by using the finite element algorithm. Results show that,under optimized structural parameters, the absorption of the absorber can reach 80% or more in the range of 5.6-14.5 μm when the incident angle range is 0° -75°. The absorber designed herein is expected to be applied to the sensing and stealth aspects at the mid-infrared band.