Electrochemical data concerning electrically conductive sulfide minerals submitted to high pressure hydrothermal fluids above 150 degrees C has not been reported in spite of its significance. In this work, electrochemical impedance spectroscopy (EIS) and Tafel studies of pyrite corrosion in pure water, 3.5% NaCl solution and 0.1 M sulfuric acid with 1796 kPa O-2 at 350 degrees C, 30 MPa were conducted, with the assistance of a self-designed three-electrode electrochemical measurement set-up that can operate in high pressure hydrothermal fluids. Results show that in pure water, 3.5% NaCl solution, and 0.1 M sulfuric acid with 1796 kPa O-2, corrosion potential (E-corr) is respectively -150, -334 and -752 mV, corrosion current (I-corr) is respectively 1.44E-5, 1.95E-4 and 7.73E-3 A. The solid-liquid interface information at pyrite surface achieved by EIS measurements reveals an important reason of the difference between the values of E-corr and I-corr in the three studied fluids. The electrochemical studies in this work also provide a promising method for research into the corrosion of other conductive sulfide minerals in high pressure hydrothermal fluids.