Natural pyrites contain high levels of adsorbed and structurally incorporated arsenic (As), which may simultaneously result in the release of As and affect the oxidation process of pyrite. However, the oxidation and electrochemical behaviors of As on the oxidation reactivity of pyrites are still not clear. In this study, pyrite was prepared by a hydrothermal method and applied to study the oxidation mechanism between pyrite and aqueous arsenate. Analyses of X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy demonstrate that the as-prepared sample is an octahedron-like pyrite with high purity and crystallinity. The interaction between As(V) and pyrite as well as the electrochemical behaviors of pyrite oxidation in the presence of aqueous arsenate were investigated under acidic conditions by an ion analysis method, cyclic voltammetry (CV), Tafel, and electrochemical impedance spectroscopy (EIS). The results of the chemical reaction indicate that electrons are transferred from S₂²⁻ to dissolved oxygen with the formation of SO₄²⁻ in the initial As(V) concentration range of 0–0.3 mmol/L. In the initial As(V) concentration range of 0.4–1.2 mmol/L, electrons are transferred from S₂²⁻ to As(V) with the formation of elemental S⁰ and As(III). The CV, the Tafel plot and EIS analyses indicate that aqueous arsenate in an electrolyte promotes oxidation reactivity and passivation of the pyrite electrode. Moreover, the electron transfer rate increases with increasing aqueous arsenate concentration in the electrolyte.