In this study, the authors investigated the electronic structures of Fe- and/ or Cd-doped sphalerite ZnS by first-principles calculations. Theoretical results show that the band gap of pure sphalerite is 2.85 eV. The results show that Fe-doped sphalerite ZnS with a doping amount of 3.125% has a band gap of 2.58 eV, and the hybridization of Fe 3d and S 3p orbital introduces two intermediate bands in the middle of the forbidden band. With the increase of the amount of Fe-doped, the width and peak height of intermediate bands also increase. The band gap of Cd-doped sphalerite is reduced to 2.68 eV, and the intermediate band below the bottom of the forbidden band is due to the hybridization of Cd 4d and S 2p orbital. Fe- and Cd-codoping reduces the band gap of sphalerite to 2.49 eV, and two donor levels in band gap can improve responding capability to visible light of sphalerite. These results provide theoretical supports for better understanding of photocatalytic mechanism of Fe- and Cd-doped natural sphalerite under visible light.