VO_2-x nanopowders were successfully synthesized with different oxygen content. The effects of oxygen content on the crystal lattice and phase transition properties were obtained form the experiment. Our result shows that vanadium interstitials are formed in oxygen-deficient samples, while oxygen interstitials are formed in the samples with excess oxygen. Both factors result in the expansion of the volume in the crystal unit cell. And the defects induce anisotropy in the lattice, which is observed in the deformation of the crystal grains with different oxygen content. The redistribution of electronic strucure in the energy band may be one of the factors that result in the changes of phase transition properties in VO_2-x.