Abstract: E-pH diagrams of FeS2-H2O system and FeAsS-H2O system at 298.15 K were drawn to provide the thermodynamic basis for the pretreatment of pyrite and arsenopyrite before leaching. According to E-pH diagram of FeS2-H2O system, pyrite can be decomposed by O2 and other oxidants. The stable region of sulfur element is small and sulfur exists as HSO4^- and SO4^2- basically in the stable region of water. According to E-pH diagram of FeAsS-H2O system, the decomposition of arsenopyrite is easier than pyrite. Oxidation potential was improved to oxidize sulfur and arsenic to be removed and avoid the formation of arsenite and sulfur elements during the pretreatment process. Verification of pressure oxidation was carried out with refractory gold ore. When the temperature, concentrate particle size, oxygen partial pressure, initial acid concentration, liquid-solid mass ratio, reaction time and stirring speed are 180°C, -0.075~+0.061 mm, 0.8 MPa, 60 g/L, 4:1, 120 min and 600 r/min respectively, average desulfurization rate is 93.85% and average arsenic removal rate is 95.91%. The experiment results are in good agreement with the calculation results of E-pH diagram.