Supported metal catalysts have been widely applied and commonly fabricated through the H2 reduction process. Herein, we develop a H2‐free room‐temperature discharge‐driven reduction (RT‐DR) reactor for fabricating supported metal catalysts at room temperature without H2. By RT‐DR reactor, a catalyst with pseudo‐boehmite (PB) as support (CdS/Pt/PB) is fabricated. In visible‐light‐driven photocatalytic H2O splitting to H2, CdS/Pt/PB shows a H2 evolution rate of 1132 μmol h−1, which is greatly enhanced than that on catalyst prepared by traditional H2‐reduction (633 μmol h−1). RT‐DR reactor is also used to prepare a catalyst with low sodium PB (LSPB) as support (CdS/Pt/LSPB). In visible‐light‐driven photocatalytic H2O splitting to H2, CdS/Pt/LSPB shows a H2 evolution rate of 2554 μmol h−1, which is 2.5 times higher than that on catalyst prepared by traditional H2‐reduction (1029 μmol h−1). Thus, RT‐DR reactor has high efficiency and universality in preparing catalysts, thus offering a great potential for commercialization.