Plasmon-mediated photocatalysts composed of Au nanoclusters and ultrathin Zn_0.5Cd_0.5S nanorods (Au/ZCS NRs) were synthesized by a facile method. All Au/ZCS samples present significant improvement for the degradation of dyes under visible light. The enhancement mechanism is different with Au content. The improved photoactivity of Au/ZCS-0.5 NRs with Au nanoclusters decorated on the lateral surface of ZCS NRs is attributed to the efficient plasmon-induced resonance energy transfer (PRET) from Au nanoclusters to ZCS NRs, which allows for the generation of more e⁻/h⁺ pairs with prolonged PL lifetime. With the increase of the Au content (2%), larger Au NPs can be decorated on the tip of ZCS NRs. The transfer of photogenerated electrons from ZCS NRs to Au becomes more significant, corresponding to the quench of PL spectra. The Au/ZCS-0.5 NRs exhibit the fastest and highest degradation efficiency under visible light. For orange G (10 ppm), the degradation rate can reach up to 98% within only 3 min. Even at up to 50 ppm, 10 mg of Au/ZCS NRs can still photodegrade about 90% of the OG dye under visible light within 8 min. This makes it possible to use less photocatalysts to degrade more recalcitrant dyes in a short time.