A new broadband tunable metamaterial absorber based on different radii of vanadium dioxide (VO2) rings loaded on the dielectric layer is designed. According to the insulator-to-metal phase transition characteristics of VO2 under thermal excitation, the dynamic adjustment of the absorption by the external temperature is achieved. The simulation results demonstrate that when VO2 is in its metal phase at high temperature, an absorption greater than 90% in the bandwidth range of 2.64-7 THz can be obtained and its relative bandwidth is reached to 90.5%. However, the absorption rate in the same frequency range is always lower than 2.3% when VO2 is in the insulator phase at low temperature, which means that the absorber can be used as a perfect reflector. The maximum tunable range of the proposed absorber can be realized from below 2.3% to nearly 100%. We further analyze and discuss the equivalent impedance and electric field distribution of the absorber and clarify the adjustment mechanism of the absorption performance of the VO2 ring. In addition, a multireflection interference theory is also investigated to quantitatively explain the physical absorption mechanism. Such a tunable broadband absorber based on temperature control has great potential to be applied to sensors, thermophotovoltaics, and wireless communication.