A temperature-voltage bi-controllable broadband polarization conversion/absorption metasurface based on vanadium dioxide (VO₂) and graphene is proposed. The control of the polarization conversion and absorption function can be realized by regulating the conductance properties of VO₂ and graphene in the metasurface. The results show that when VO₂ is in metal state and graphene is in insulating state, the metasurface operates in the broadband polarization conversion mode, achieving linear polarization conversion in the range of 1.57--2.49 THz. When VO₂ is in insulating state and graphene is in metal state, the operation mode of the metasurface is switched to the absorption mode, and the absorptivity reaches 90% in the range of 1.56--2.99 THz. The polarization conversion and absorption performance can be controlled by regulating the temperature of VO₂ and the bias voltage of graphene, respectively. Furthermore, the working principle of the metasurface is explained by eigenmodes, impedance matching theory, and current and magnetic field distributions. The stability of its performance under different structural parameters and incident angles is also discussed.