The design of tunable and multifunctional metastructures (MSs) is currently a trend in the terahertz (THz) field. Based on the characteristic that thermal excitation can cause the phase transition of vanadium dioxide (VO2), a MS that concentrates both cross-polarization conversion and absorption functions is proposed in this paper, and switching two functions can be achieved by controlling the temperature. At high temperatures (68°C), the proposed MS exhibits a narrow-band absorption function in the range of 0.67 THz-0.95 THz. When the temperature drops below 68°C, VO2 is in the insulated state, and the structure can be considered as a polarization converter. Simulation results indicate that the broadband cross-polarization conversion can be realized in 0.69 THz-1.38 THz with a polarization conversion ratio above 90% and a relative bandwidth of 66.7%. This paper analyzes the amplitude, phase, and surface current distributions under the polarization conversion function, as well as the impedance, power loss distributions, and equivalent circuits under the absorption function. In addition, the angular stability and the influences of the structural parameters on performance are also discussed. The proposed MS is suitable for complex applications due to its tunability and dual functionality.