Abstract: TiO₂ nanopowders doped by the lanthanum trivalent ion were prepared by plasma thermal spray with solution of titanium tetra-tert-butoxide.And TiO₂ were characterized by XRD, XPS TEM and UV-Vis.The photocatalytic activities were also investigated. The results showed that the prepared doped powders are the mixture structure of anatase and rutile.La³⁺ doping can promote the transformation of TiO₂ from anatase to rutile, at the same time, it can restrain TiO₂ particle growing up.La³⁺ doping greatly increases the photocatalytic activity of TiO₂, the optimal doping concentration was 0.5%, and the degradation rate of methyl orange is 82.4%, which is 13.2% higher than that with pure TiO₂.