•The intrinsic 1T-TaS2 is a metallic material without band gap.•When the torsion angle reaches 10°, we found a narrow split-off band above the Fermi level.•The torsion causes a significant increase in the static dielectric constant.•When the torsion angle reaches 18°, the electronic structure and optical constants change significantly due to the fracture of original bonds. The optoelectronic properties of monolayer 1T-TaS2 at 0∼20° torsion are systematically studied, including the band structure, density of electronic states, complex dielectric function, absorption and reflection spectra based on first-principles calculations. We found that a split-off bandgap above the Fermi level by torsional deformation and increases with torsion. The analysis of the optical properties reveals that the static dielectric constant, absorption peak, and reflection peak in the low-energy region increases with torsion. When the torsion angle reaches 18°, the electronic structure and optical constants change significantly due to the fracture of original bonds. This paper provides a theoretical reference for the subsequent application of single-layer 1T-TaS2 in the sensor design.