A terahertz absorber comprising a circular resonant ring structure with four response frequency bands has been designed based on the principle of different responses of resonant rings exhibiting different sizes and shapes to electromagnetic fields. In this study, the absorber characteristics are studied using the finite-difference time-domain method. The terahertz absorber is designed and simulated by changing the geometrical size of the top metal ring pattern, the thickness of the dielectric layer in the middle layer, and the change rate of the silicon conductivity at the top metal ring. When the terahertz absorber is coupled with a multi-frequency absorber, the absorption at low frequencies reaches perfect absorption and the absorption rate at high frequencies increases from 70% to 94%; further, the low-frequency shifts from 0.775 THz and 1.064 THz to 0.697 THz and 1.017 THz, respectively, with a change in conductivity. The frequencies of 78 GHz and 47 GHz are shifted to achieve continuous frequency tuning.