Photoelectrochemically splitting water to hydrogen(H2)and oxygen(O2)driven by solar has been attracted more attention because it was considered a potential solution for supplying the worlds growing population with clean,affordable energy.[1-4] In this work,we made Au nanopattern with different size on p-Si wafer by localized Galvanic displacement using block copolymer template,then deposition different Pt on Au nanopattern by controlled seed growth to fabricate photocathode.The photocathodes with different size and distribution of Au/Pt core/shell nanopatterns make us to gain better insight on how the geometric and electronic affect photoelectrochemical activities.