Plasmonic AuCu bimetallic nanoparticles supported on monoclinic CaIn2S4 have been synthesized through the photoreduction method, by which AuCu bimetallic nanoparticles with different atomic arrangements were site-selectively photo-deposited at the edges of CaIn2S4 surface nanosteps. The obtained plasmonic composites were characterized by XRD, TEM, photoelectrochemical analysis, XPS, UV-vis and PL spectroscopy. The results showed that AuCu bimetallic nanoparticles with alloy structure showed better performance for light absorption, charge separation and photocatalytic activity compared to AuCu core-shell structure. Especially, alloyed Au0.4Cu0.1/CaIn2S4 composite exhibited the highest visible activity for hydrogen production from Na2S/Na2SO3 solution with a rate of 452.8 mu mol/h, over 2.2, 10.0, 63.8 and 76.7 times higher than that of core-shell Cu-0.1/Au-0.4/CaIn2S4, Au-0.3/CaIn2S4, Cu-0.3/CaIn2S4 and CaIn2S4, respectively. The enhanced photocatalytic performance of AuCu/CaIn2S4 composites could be mainly ascribed to the synergistic effect in AuCu bimetallic nanoparticles and the surface plasmon resonance effect of Au.