Bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is mandatory for clean and sustainable alternative energy sources. To improve the efficiency of the overall water splitting, highly efficient and stable bifunctional electrocatalysts in acidic media is vital for polymer electrolyte membrane (PEM) electrolyzers. Herein, we synthesized cactus like Cu2-xS@IrSy@IrRu (CIS@IrRu) alloy nanoparticles via template mediated method, which show highly efficient HER and OER electrocatalytic activity. Due to the dendritic structure and stable IrSy shell, the cactus like CIS@IrRu nanoparticles exhibit highly efficient HER and OER catalytic activity in acidic media. The CIS@IrRu nanoparticles show the Ir/Ru composition dependent electrocatalytic activity with best bifunctional performace at the Ir ratio to Ru is 1.00 to 1.07. More significantly, in the overall water splitting, CIS@Ir0.48Ru0.52 reach 10 mA cm-2 at the voltage of 1.56 V in 0.1 M HClO4 electrolyte and maintain high electrocatalytic activity after durability test without structural deformation.