Photocatalytic technology is a new method for environmental pollution control, but its application has been limited for low quantum conversion efficiency and requiring UV light to excite photocatalytic activity. To solve the problems, a large number of experimental studies have been carried out and some achievements have been obtained, especially the theoretical study developed in recent years that has attracted attentions and promoted the development of photocatalytic technology. Main theoretical results on ion doping anatase TiO 2 photocatalyst reported in literatures and by our group are reviewed. The influences of different ions doping or codoping on TiO 2 crystal structure, energy band, optical and photocatalytic properties are summarized. Methods on how to choose appropriate doping ions have been suggested for effectively improving TiO 2 photocatalytic property.