Nanosized　Pd-based　catalysts　are　widely　used　in　the　direct　hydrogen　peroxide　(H2O2)　synthesis　from　H-2　and　O-2,　while　the　selectivity　and　yield　of　H2O2　remain　inferior.　Here,　a　remarkable　H2O2　yield　of　115　mol/g(Pd)/h　and　H2O2　selectivity　higher　than　99%　are　reported　using　a　Pd　single-atom　catalyst　for　the　direct　synthesis　of　H2O2.　Nanosized　palladium　(Pd)-based　catalysts　are　widely　used　in　the　direct　hydrogen　peroxide　(H2O2)　synthesis　from　H-2　and　O-2,　while　its　selectivity　and　yield　remain　inferior　because　of　the　O-O　bond　cleavage　from　both　the　reactant　O-2　and　the　produced　H2O2,　which　is　assumed　to　have　originated　from　various　O-2　adsorption　configurations　on　the　Pd　nanoparticles.　Herein,　single　Pd　atom　catalyst　with　high　activity　and　selectivity　is　reported.　Density　functional　theory　calculations　certify　that　the　O-O　bond　breaking　is　significantly　inhibited　on　the　single　Pd　atom　and　the　O-2　is　easier　to　be　activated　to　form　*OOH,　which　is　a　key　intermediate　for　H2O2　synthesis;　in　addition,　H2O2　degradation　is　shut　down.　Here,　we　show　single　Pd　atom　catalyst　displays　a　remarkable　H2O2　yield　of　115　mol/g(Pd)/h　and　H2O2　selectivity　higher　than　99%;　while　the　concentration　of　H2O2　reaches　1.07　wt.%　in　a　batch.