Direct synthesis of H2O2 from H2 and O2 can avoid the energy and environmental problems of current multi-step anthraquinone oxidation process by enabling high atom utilization and generating only a water by-product. However, the direct process suffers a low H2O2 yield, and it is challenging to suppress the unfavorable side-reactions in the absence of corrosive additives under the restriction of explosion limits. In this study, an efficient new catalyst was prepared by immobilizing Pd nanoparticles (NPs) on an acidic hyper-crosslinked porous polymer (HCPP). The Pd catalyst supported on HCPP functionalized with both carboxylic and sulfonic acids (Pd/c-s-HCPP) achieved as high as 3130 mmol H2O2/g Pd.h with 82% selectivity to H2O2, which corresponded to one of the best catalysts reported so far. Pd/c-s-HCPP showed superior catalytic performance when compared with ones by Pd NPs supported on unfunctionalized HCPP (Pd/HCPP), or sulfonated resin (Pd/SO3H-resin). Extensive characterizations and H2 adsorption measurements indicated that the c-s-HCPP provided (i) selective adsorption sites for Pd precursors, (ii) acted as an efficient H2 reservoir in the proximity of the small Pd NPs formed, and (iii) imparts solid acidity to enhance H2O2 selectivity, which offered a new direction in the catalyst design for the direct synthesis of H2O2.