Hydrogen evolution reaction (HER) plays an indispensable role in hydrogen economy. However, the development of highly active and durable Pt catalysts remains a great challenge. A homogenously‐dispersed, ultrafine and chemically anchored Pt‐based catalyst is successfully synthesized with the regulation of ‐SH groups tethered to SBA‐15 template. The ‐SH not only regulates the particle size of Pt, but also modifies the chemical environment of the carbon support by converting itself into heteroatom—S. The obtained catalyst (Pt/OMCSH) exhibits superior HER catalytic activity (15.4 mV at 10 mA cm−2; 28.4 mV dec−1; 1.0 M KOH) and stability to benchmark samples and most of the previously reported Pt‐based electrocatalysts. First‐principles calculations reveal that the presence of S in the carbon support regulates the electronic structure of Pt and strengthens the metal‐support interaction, thus boosting the reaction kinetics and enhancing the stability of Pt/OMCSH catalyst for HER. [ABSTRACT FROM AUTHOR]