A bi-function switchable metasurface structure is proposed to realize dynamic switch function between ultrabroadband terahertz absorber and polarization converter. The structure consists of a SO₂ hemisphere in a square lattice, two different radius hybrid gold-photosensitive silicon rings cladding configuration, and metal substrate. When the conductivity of the photosensitive silicon is 1.0  ×  10⁴  S  /  m (i.e., in the metallic state), the metasurface structure exhibits ultrabroadband terahertz absorber with above 90% absorption in the range of 3.96 to 10.0 THz. The high absorption performance can be maintained before incident angle of 50 deg. When the conductivity of the photosensitive silicon is 2.5  ×  10^−  4  S  /  m (in the dielectric state), the proposed structure serves as a terahertz polarization converter. The polarization conversion rate (PCR) is larger than 90% from 3.88 to 7.21 THz within the incident angle range of 0 deg to 80 deg. By changing the conductivity of the photosensitive silicon, absorbance and PCR can be dynamically adjusted. The scheme provides a new perspective to explore multifunction terahertz device.