A simple and efficient light-assisted method is employed to prepare powder samples of all-inorganic mixedperovskite CsPbBr3-xIx from CsPbBr3-xIx by ion exchange in aqueous HBr/KI solution such that the concentration of I in a sample particle decreases on going from the surface to the interior. CsPbBr3-xIx/Pt, namely, CsPbBr3-xIx samples loaded with Pt nanoparticles, shows a high performance for the hydrogen evolution under visible-light irradiation in aqueous HBr solution saturated with CsPbBr3. The H-2 evolution rate of the CsPbBr3-xIx/Pt powders (200 mg) is determined to be 224 mu mol h(-1), under 120 mW cm(-2) visible-light (lambda >= 420 nm) illumination. The CsPbBr3-xIx. samples have a high stability, with no apparent decrease in the catalytic activity after 50 h of repeated H-2 evolution experiments. The apparent quantum efficiency of CsPbBr3-xIx /Pt is determined to be 2.15% under the irradiation of 450 nm light.