A strategy of reaction-environment modulation was employed to change the surface property of a semiconductor photocatalyst to enhance its photocatalytic performance. Surface alkalinization induced by a high alkalinity of the solution environment significantly shifted the surface energy band of a SrTiO3 photocatalyst to a more negative level, supplying a strong potential for H2O reduction and consequently promoting the photocatalytic efficiency of H-2 evolution. This mechanism is also applicable for visible-light-sensitive La,Cr-codoped SrTiO3 photocatalyst, which hence, could achieve a high apparent quantum efficiency of 25.6% for H-2 evolution in CH3OH aqueous solution containing 5 M NaOH at an incident wavelength of 425 +/- 12 nm.