The energy band structure, density of electronic state and absorption of S-doped wurtzite ZnO are investigated using first-principles based on density functional theory. These results indicate that the crystal lattice parameters increase with increasing doping ratio. Nevertheless, the electron mobility is enhanced as the band gap decreasing by S-doping. Optical properties further calculated show that, absorption spectrum shift to the red side after S-doping. Absorption spectrum peak increases with increasing of the S-doped amounts, so that the visible light and ultraviolet region of the light absorption are improved.