In this work, we have shown that aluminium acetylacetonate (Al(acac)(3)) can be used as the catalyst to synthesize Ti3+ self-doped TiO2 (Ti3+-TiO2) by sol-gel method in air. Ti3+-TiO2 can be obtained directly and Al(acac)(3) is removed during the annealing process. Ti3+ concentrates in the surface layer of powders, making a homo-junction between Ti3+-TiO2 in the surface layer and TiO2 in the bulk. Based on the scheme of Zielger-Natta catalysts and the characterization of the sols and gels of samples, the synthesis mechanism of Ti3+ is proposed as the combination of steric hindrance effect, Lewis acid-base reaction and crystal field effect and Al(acac)(3) acts as the catalyst in the reaction. Charge generation, charge transport and interface reactions, all of the three crucial strategies of photocatalytic are improved through the self-doped Ti3+, resulting in enhanced photocatalytic and photoelectrochemical activities. Compared with the reported methods, this work proposes a simple and novel route for the preparation of Ti3+-TiO2, which would facilitate the preparation and application of TiO2 photo-catalyst.