Plasmonic gold (Au) and Au-based nanocatalysts have received significant attention over the past few decades due to their unique visible light (VL) photocatalytic features for a wide variety of chemical reactions in the fields of environmental protection. However, improving their VL photocatalytic activity via a rational design is prevalently regarded as a grand challenge. Herein we boosted the VL photocatalysis of the TiO2-supported Au-Cu nanocatalyst by applying O2plasma to treat this bimetallic plasmonic nanocatalyst. We found that O2plasma treatment led to a strong interaction between the Au and Cu species compared with conventional calcination treatment. This interaction controlled the size of plasmonic metallic nanoparticles and also contributed to the construction of AuCu-TiO2interfacial sites by forming AuCu alloy nanoparticles, which, thus, enabled the plasmonic Au-Cu nanocatalyst to reduce the Schottky barrier height and create numbers of highly active interfacial sites. The catalyst’s characterizations and density functional theory (DFT) calculations demonstrated that boosted VL photocatalytic activity over O2plasma treated Au-Cu/TiO2nanocatalyst arose from the favorable transfer of hot electrons and a low barrier for the reaction between CO and O with the construction of large numbers of AuCu-TiO2interfacial sites. This work provides an efficient approach for the rational design and development of highly active plasmonic Au and Au-based nanocatalysts and deepens our understanding of their role in VL photocatalytic reactions.