Hydrogen production has been considered as the most promising approach for obtaining sustainable and clean energy source. Modification of TiO2 photocatalyst with the aim of enhancing the photocatalytic efficiency has always been the top importance. In this work, Tin ions have been used as dopant to adjust the crystal phase and to improve the catalytic performance of TiO2. The results showed that Sn4+ doping transferred the mixed phase TiO2 photocatalyst into single rutile phase TiO2 and increased the water splitting efficiency. Photoluminescence, X-ray photoelectron spectroscopy and UV–vis spectrometer characterization suggested that charge transfer between Ti4+ and Sn4+ is the key reason for the suppression of carrier recombination and the improvement of the photocatalytic efficiency. Sn2+ doping did not adjust the rutile/anatase mix phase formation considerably, charge transfer from Ti4+ to Sn4+ is also proved to be the reason for the slightly enhanced water splitting efficiency. This work suggests that the ion valence of tin is the critical factor affecting the photocatalytic performance of TiO2.