The mechanism of deactivation and regeneration of the Pt/b-TiO2 NFs photocatalyst in photocatalytic pure water splitting was studied systematically. The photocatalyst is deactivated due to the accumulation of product H2 inhibits the forward reaction and gradual substitution of H2O2 for H2O in the absorption site on the Pt/b-TiO2 NFs surface. Timely removal of H2 allows the photocatalysts to operate stably for more than 500 h. And the H2O2 can be desorbed by bubbling with Ar gas at 120 ℃.