The atomic and electronic structure of anatase TiO₂ with impurity of N,C and S are studied by first-principles pseudopotential calculations based on density-functional theory (DFT) in this paper. The results show that the impurity react oxidation and the nearby Ti atoms react reduction. By analyzing band structure,density of states and charge population,it is concluded that an impurity band appears in the gap and Fermi energy goes up. The spectrum generates red shift and the activity of photocatalysis heightens because of the gap decreasing. The response of wavelength reaches the range of visible light.