Pure anatase, pure rutile and the mixed TiO2 crystals with different amounts of rutile and anatase were prepared by a hydrothermal method using Ti (OBu)4 as starting material. The effect of anions on crystal phase and morphology of TiO2 synthesized by the hydrothermal method was investigated, and the relevant mechanism was also discussed. The X-ray diffraction (XRD) results indicate that Cl- ion was in favor of the formation of rutile, while NO3- and CH3COO- were beneficial for the formation of anatase. The hydrothermal conditions have significant effects on the phase component, morphology, and particle size of obtained titania products. Additionally, mixed TiO2 crystals with different amounts of rutile and anatase could be prepared by adjusting the reaction conditions, such as the concentration of Cl- ion, hydrothermal time, the amount of citric acid and the concentration of tetrabutyl titanate.