The polycrystalline nano-TiO₂ was synthesized by the gaseous-liquid detonation (GLD) method using H₂, O₂, and TiCl₄ as the mixture precursors. The effects of different molar ratios of precursors and initial reaction pressures on the nano-TiO₂ crystalline structures were studied. The nanocrystal structures, components, particle size, and morphology were characterized by the X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results demonstrate that the nano-TiO₂ consists of pure anatase-TiO₂, pure rutile-TiO₂, and the mixtures of spherical or quasi-spherical morphologies with particle size of 20~150 nm. Furthermore, the formation mechanism of nano-TiO₂ by GLD method was analyzed. The relevant GLD parameters were calculated based on the C-J theory and the related chemical reaction data, which effectively verifies the influence of different molar ratios of precursors and initial pressures on the controllable synthesis of polycrystalline nano-TiO₂.