WS2 has attracted extensive attention due to its excellent physical and photoelectric properties. Based on the first-principle calculation method, electronic structure and optical properties of the intrinsic monolayer WS2 and the Y doped WS2 with different concentration of Y atoms substitutionally doped in W atom-site were investigated. The results show that the intrinsic monolayer WS2 is a direct band gap semiconductor with 1.814 eV of band gap. After 4% concentration (atomic fraction) of Y doping, the band gap reduces to 1.508 eV, and the direct band gap characteristics are still maintained. As the doping concentration increases, the band gap of the doped WS2 further decreases. When the concentration reaches 25%, the band structure transforms into indirect with the band gap of 0.658 eV, and the doped WS2 exhibits magnetic properties. Appropriate concentration of doping can improve the conductivity of materials. As the doping concentration increases, the doped system maintains transparency, and the absorption efficiency in infrared and visible region together with the dielectric properties of the material significantly improve. This work provides a theoretical basis for the research of two-dimensional WS2 related optoelectronic devices.