Abstract: In this paper, a three-dimensional metamaterial absorber was designed. The upper part of the structure is composed of a cross-shaped base plate loaded with a number of square resonance rings on the side, and the bottom part is an aluminum plate as a reflecting floor. The thickness of the metamaterial absorber is 11 mm. The numerical simulation results shows that the multi-frequency resonant absorption is changed to broadband absorption by adding lumped resistance. The absorption rate is more than 90% and the relative bandwidth is 84.4% in the frequency range of 5.62 GHz～ 13.90 GHz. The metamaterial absorbers have excellent wide-angle absorption characteristics in TM（Transverse Magneticwave） mode. The equivalent electromagnetic parameters were calculated by S parameter retrieved. The results show that the broadband absorption mechanism of metamaterial absorber is based on good impedance matching and electromagnetic resonance. Combined with the field diagram of resonant frequency, it is further verified that the energy loss of electromagnetic resonance is transformed to ohmic loss of the lumped resistors. The simulation results of square resonant ring as a single resonant structure show that the broadband and efficient absorption of the composite resonant structure is due to the superposition and coupling of each resonant ring.