The tin oxide nanopowder is synthesized by hydrothermal method and the hydrothermal time effect on its phase structure, morphology and optical properties are studied. The results show that the samples are all tetragonal rutile structure with high purity, and possess flowers-shaped morphology. The crystallites size increases as the hydrothermal time does. The sample obtained through 12 h hydrothermal time has excellent morphology, uniform size and great dispersibility. Photoluminescence spectra shows photoluminesce peak appear near 500 nm, which is related to the oxygen vacancy. With the increase of hydrothermal time, the photoluminesce peak has a blue shift and the peak intensity decreases.