In this work, we mainly investigate the influence of structure water on crystal structure, electronic structure, band structure, and charge separation of WO3 center dot 2H(2)O. It is found, for the first time, that although water is a weak electron donor, a ligand-to-metal charge transfer (LMCT) from H2O to W occurs. The structure water contributes to the conduction band (CB) of WO3 center dot 2H(2)O, and the band gap of WO3 center dot 2H(2)O is obviously narrowed, thus increasing the light absorption obviously. Moreover, the results of EIS, photocurrent spectra, and PL show that structure water in WO3 center dot 2H(2)O also improves the charge separation and transfer efficiency of the catalyst. This is the first investigation on the LMCT transfer from structure water (a weak electron donor) to tungsten, which obviously improves light absorption and charge separation. Under visible light irradiation (lambda >= 420 nm), WO3 center dot 2H(2)O nanosheets have a photocatalytic activity 2.3 times higher than that of WO3 for the degradation of methylene blue (MB). The kind number of photochemical materials can be increased greatly, because structure water-contained compounds widely exist in nature.