The terahertz technology has attracted considerable attention because of its potential applications in various fields.However,the research of functional devices,including polarization converters,remains a major demand for practical ap-plications.In this work,a reflective dual-functional terahertz metadevice is presented,which combines two different polar-ization conversions through using a switchable metasurface.Different functions can be achieved because of the insulator-to-metal transition of vanadium dioxide (VO2).At room temperature,the metadevice can be regarded as a linear-to-linear polarization convertor containing a gold circular split-ring resonator (CSRR),first polyimide (PI) spacer,continuous VO2 film,second PI spacer,and gold substrate.The converter possesses a polarization conversion ratio higher than 0.9 and a bandwidth ratio of 81％ in a range from 0.912 THz to 2.146 THz.When the temperature is above the insulator-to-metal transition temperature (approximately 68 ℃) and VO2 becomes a metal,the metasurface transforms into a wideband linear-to-circular polarization converter composed of the gold CSRR,first PI layer,and continuous VO2 film.The ellipticity is close to-1,while the axis ratio is lower than 3 dB in a range of 1.07 THz-l.67 THz.The metadevice also achieves a large angle tolerance and large manufacturing tolerance.