The photocatalytic mechanism, catalogue and carrier of photocatalysts and its applications were described in this paper. According to their composition and structure, the photocatalysts are classified as simple oxide-type, nanometer sulfide, composite oxides, layer structure compound, AB2O4-type , complexes photocatalysts and so on. The development direction of photocatalyst is analyzed. The methods of improving the properties of photocatalysts and the factors influencing photocatalytic efficiency were discussed too.