Terahertz technology has garnered significant attention from researchers due to its outstanding properties and potential. Currently, terahertz waves are extensively used in various fields, including communications, medical imaging, radar, and more. As a result, terahertz technology plays a crucial role in the advancement of modern society. Alongside terahertz technology, metamaterials have also emerged as a key area of research. Traditional natural materials possess certain inherent limitations, such as difficulty in modifying their structures, limited operational ranges, and fixed properties. In contrast, metamaterials offer superior characteristics and advantages. These artificial composite materials, designed with tailored structures, can be easily fabricated and modified to meet specific operational requirements. Metamaterials exhibit extraordinary physical properties that natural materials do not, overcoming the limitations of conventional materials and providing new possibilities for technological innovation. Currently, metamaterials are widely applied in areas such as lenses, energy absorption, and antennas. When integrated with terahertz technology, metamaterials enable the design of advanced devices, including absorbers, filters, and sensors, further expanding the potential of terahertz applications. Vanadium dioxide (VO?) exhibits remarkable phase transition characteristics. When external factors like temperature, electric field, or light field are altered, the conductivity of vanadium dioxide can change by 4 to 5 orders of magnitude, triggering a phase transition. Building on these phase transition properties, this paper proposes a multifunctional device based on vanadium dioxide metamaterials. This device is capable of achieving three key functions: broadband absorption, linear-to-circular polarization conversion, and linear-to-linear polarization conversion. Additionally, the device allows for switching between these functions by altering the external environment. Simulations and data analysis are carried out using the commercial software CST Studio Suite in the frequency range of 0.1 to 6 THz. The results show that when the conductivity of vanadium dioxide is 2×10? S/m, it is in its metallic state, and the designed structure achieves broadband absorption in the frequency range of 2.11~4.89 THz, with a relative bandwidth of 79.43%. When the conductivity of vanadium dioxide is reduced to 20 S/m, it transitions to an insulating state. The structure designed in this paper achieves Linear-To-Circular (LTC) polarization conversion across multiple frequency bands, including 1.02~1.21 THz, 1.39~2.34 THz, 2.81~3.44 THz, and 3.60 THz. It also enables Linear-To-Linear (LTL) polarization conversion in the frequency ranges of 1.21~1.39 THz, 2.46~2.81 THz, and 3.44~3.57 THz. Additionally, the paper investigates the effects of terahertz wave incidence angle and polarization angle on the structural absorption, as well as how structural parameters influence both absorption and polarization conversion characteristics. The results show that, when the incidence angle is within the range of 0° to 40°, the designed structure maintains high absorption performance. Furthermore, the absorption performance remains unaffected by changes in the polarization angle, demonstrating that the device exhibits polarization insensitivity. In summary, the device proposed in this paper not only realizes the three functions of broadband absorption, linear-to-circular polarization conversion, and linear-to-linear polarization conversion, but it also features a simple design and is easy to manufacture. These advantages position the device as a promising candidate for potential applications in terahertz communication, imaging, and other intelligent fields.