Abstract: The development of \rmBi_2W\rmO_6-based materials has become one of research hotspots due to the increasing demands on high-efficient photocatalyst responding to visible light. In this work, the effect of high energy radiation (\gamma-ray) on the structure and the photocatalytic activity of \rmBi_2W\rmO_6 nanocrystals was first studied. No morphological change of \rmBi_2W\rmO_6 nanocrystals was observed by SEM under \gamma-ray radiation. However, the XRD spectra of the irradiated \rmBi_2W\rmO_6 nanocrystals showed the characteristic 2\theta of (113) plane shifts slightly from 28.37^\rmo to 28.45^\rmo with the increase of the absorbed dose, confirming the change in the crystal structure of \rmBi_2W\rmO_6. The XPS results proved the crystal structure change was originated from the generation of oxygen vacancy defects under high-dose radiation. The photocatalytic activity of \rmBi_2W\rmO_6 on the decomposition of methylene blue (MB) in water under visible light increases gradually with the increase of absorbed dose. Moreover, the improved photocatalytic performance of the irradiated \rmBi_2W\rmO_6 nanocrystals remained after three cycles of photocatalysis, indicating a good stability of the created oxygen vacancy defects. This work gives a new simple way to improve photocatalytic performance of \rmBi_2W\rmO_6 through creating oxygen vacancy defects in the crystal structure by \gamma-ray radiation.