The performances of metamaterial absorbers can be affected by the incidence angle of electromagnetic wave. It is difficult to design the incidence angle-insensitive metamaterial absorbers. In this paper, we propose a metamaterial absorber with wide-angle incidence based on the equivalent medium theory. The absorber unit consists of a double-sided split resonant ring placed vertically on the ground. The resistors and capacitors are loaded at the opening of the resonant ring. The resistor is used to adjust the equivalent electromagnetic parameters of the metamaterial, and the capacitor is used to control the resonant frequency of the metamaterial and miniaturize the unit. When the transverse electric (TE) plane wave impinges on the surface of the absorber, R = 4000 Ohm and C = 1.5 pF, the proposed absorber can achieve an absorptivity greater than 90% at 1.59 GHz up to an incidence angle reaching 70°. Besides, the absorber can achieve an 85% absorptivity under an incidence angle of 75°. when the transverse magnetic (TM) plane wave impinges on the surface of the absorbers, R = 1200 Ω and C = 1.5 pF, the proposed absorber can achieve an absorptivity of greater than 90% at 1.59 GHz up to a 70°incidence angle. Besides, the absorber can also achieve an absorptivity of 85% up to 75°. The results show that the measurement results are basically consistent with the simulation results. In addition, when the capacitance is changed while the other parameters are fixed, the metamaterial absorber proposed in this paper still has the same wide-angle absorbing performance at the new resonant frequency. In other words, the proposed absorber has broadband operating characteristics. A frequency-tunable metamaterial absorber with wide-angle incidence can be designed based on the aforementioned results. The results in this paper provide a method of tuning capacitance. The opening is set at the other end of the split ring, and the same fixed-value resistor and variable capacitor are loaded on the left opening, and the corresponding DC bias feeder is designed. One end of the DC bias line is directly connected to the ground, and the other end needs to be separately connected to the other DC bias feeder of each unit to realize the control of the variable capacitors of each unit.