In electrocatalysis processes, the interactions among reactants, reaction intermediates and their products, and the surfaces of electrocatalysts are of great significance. Therefore, the tailoring of active sites has become a primary focus in the field of electrocatalysis, which directly determines the catalytic performance and cost of electro catalysis processes. Herein, the fundamentals of electrocatalysis were briefly introduced. The reaction mechanism and principles for designing high-efficiency electrocatalysts were presented using the anodic oxygen reduction reaction (ORR) of fuel cells as a typical model reaction. Recent advances and challenges in tailoring the active sites of ORR electrocatalysts were reviewed, including the structure and chemical composition, as well as the physical effects (eg. lattice-strain and electronic coupling effects) in boosting the catalytic activity and durability of Pd-based nanoalloy electrocatalysts. Finally, considering the cost of noble metal electrocatalysts and the improvements in catalytic performance in ORR processes, the perspectives on future synthetic strategies and developments of Pd-based nanoalloy electrocatalysts were presented.