A visible-light-driven hydrogen evolution system was constructed in one step with xanthene dye as photosensitizer, triethanolamine (TEOA) as electron donor, Pt as cocatalyst, and Keggin-type silicon-tungsten polyoxometalate (POM) as electron relay. The average rate of hydrogen evolution from the eosin Y−POM−TEOA−PtCl2-6 systems is 51.8 μ mol h−1, and the apparent quantum yield is 8.9% during 20 h irradiation (λ>420 nm;, a high-pressure Hg lamp was used as the light source). Ultraviolet–visible absorption spectra and fluorescence spectra were used to study the mechanism of charge transfer. A radical anion Dye−, which generates from quenching of the triplet-excited state 3Dye* by sacrificial electron donor, was considered the main species for transmitting electrons to POM and then to Pt. SiW9O10−34, derived from SiW12O4−40, is the main form of POM in our reaction system, which can mediate the electron transfer from Dye− to Pt, so an enhanced hydrogen evolution was realized. The present study highlights POM as electron relay in the photocatalytic hydrogen evolution process, which is expected to contribute to the development of functional and efficient artificial photosynthetic systems.