In this paper, a switchable terahertz metasurface based on VO2 multilayer structure is raised, which utilizes the temperature phase-transition properties of VO2 to achieve the functions of switchable polarization conversion and reflection phase modulation for arbitrarily polarized waves at different temperatures. The simulation results show that at high-temperature and low-temperature, the metasurface develop a resonant system to achieve polarization conversion for circularly polarized (CP) and linearly polarized (LP) waves, respectively. For the conversion of the CP wave at high-temperature, the polarization conversion rate exceeds 90% in the terahertz frequency range of 1.01~2.00 THz; at low-temperature, the polarization conversion of the LP wave reaches a near-perfect polarization conversion rate at frequencies f=0.65, 1.07, and 1.50 THz. Arbitrary phase regulation can be achieved by rotating the VO2 strips and altering the geometry of the C-shaped split resonator ring (CSRR) to form a periodic array with a constant gradient phase. In order to verify that the device has the function of wavefront phase modulation, we use the device to simulate the abnormal reflection based on the generalized Snell's law.Additionally, we generated a bifocal focused beam within a cross-channel in LP incidence mode using the propagation phase principle.