In this paper, a multifunctional metamaterial device based on the phase transition properties of vanadium dioxide (VO₂) is proposed. The metamaterial structure consists of a top layer combined with VO₂-filled Split Ring Resonator (SRR) and a metal cross, a polyimide (PI) dielectric layer, and a metal substrate. When the VO₂ is in the insulating state, the cross-polarization conversion function can be realized, and its Polarization Conversion Rate (PCR) is greater than 90% in the range of 0.48-0.87 THz. When the VO₂ is in the metallic state, the device can realize dual-frequency absorption and be applied in high-sensitivity sensing functions. The absorption rates are higher than 88% at the frequencies of 1.64 THz and 2.15 THz. By changing the refractive index of the sample material, the sensing sensitivities at the two related frequencies are about 25.6 GHz/RIU and 159 GHz/RIU, and the Q-factors are 71.34 and 23.12, respectively. The proposed metamaterial multifunctional device exhibits the advantages of a simple structure, a switchable function, and high-efficiency polarization conversion, and provides potential application value in future terahertz communication, imaging and other fields.