For the application requirements of multi-band and perfect absorber, a tri-band absorber based on metasurface is designed in this paper. The proposed absorber consists of a metallic pattern layer, an intermediate dielectric layer and a metallic bottom plate. The results show that the absorber has absorptivity of 99.98%, 99.94% and 99.98% at three resonant frequencies of 5.16 GHz (C-band), 7.27 GHz (C-band) and 8.32 GHz (X-band), which can achieve almost perfect absorption. The origin of three resonant frequencies is analyzed by impedance matching theory. The analysis of the surface current, electric field and magnetic field distributions are simulated at resonant frequency to explain the tri-band absorption mechanism. The regulation of single band, dual band and tri-band can be obtained by changing the number of metallic patterns on the top layer of the absorber. Moreover, the dependence of the absorptivity on polarization angle and incidence angle is studied, and the results show that the absorber has good polarization insensitivity and wide-angle stability (0°—60°). The proposed tri-band absorber based on metasurface has the characteristics of easy design and thin and light, and has great application potential in the fields of electromagnetic absorption, stealth, and sensing.