Previous studies revealed that HER activities on MoS₂ could be boosted through exotic doping to introduce active centers. However, it is difficult to dope exotic elements into MoS₂ with a high concentration due to their different chemical properties from host elements. Here, we theoretically and experimentally optimize the MoS₂ edges through substituting Mo with different concentrations of isovalent W. The simulations predict that 50% substitution of Mo by W shows the best catalytic activity because of the reduction of H adsorption free energy and facilitation of charge transfer. Experiments demonstrate that the Mo_0.5W_0.5S₂ significantly enhances HER performance of MoS₂-based compounds, having an onset potential of −37 mV and achieving 10 mA cm^–2 with an overpotential of 138 mV.