Surface mineralogy is one of the modern branches of mineralogy. The research of the interface of mineral liquid, namely the reaction of mineral liquid, is one of the most interesting and important subjects. This paper is concentrated on sulphides, which are important and common minerals in the nature. The electrochemical behaviour on the interface between sulphide and solution is the main objective in this study. A Fe1-xS-Cr6+ pile is designed to prove how hardly-dissoluble sulphides reduce Cr6+ into Cr3+. Through the measurement of electrical potential (E), t-E relation curve, the visible adsorption spectrum and the X-A relation curve of Cr6+ solution, the problem has been solved. According to computer retrieval of previous references and data, no such eletro-chemical analysis has ever been used in the research of the interface reaction between natural sulphide minerals and solution. A number of valuable results, not only theoretical but also actual, have been gained from the research. In short, the results show that the electrochemical effect on sulphide liquid interface, which is of great significance, can be applied to the treatment of environmental pollutants, the studies of reaction kinetics of metallic minerals and mechanism of metallic deposits and so on.