Abstract: The process of oxidizing pyrite by leaching bacterium is such a process that the old chemical bond is broken with new chemical bond formed by leaching bacterium on the pyrite crystal surface. The interfaces between leaching bacterium solution and natural pyrite produce a series of biochemical reactions. Because of the different distribution patterns and densities of Fe²⁺ and [S2]^2- of pyrite on crystal faces (100), (110) and (111), the extensions of their bio-oxidation and corrosion are also different. The process of pyrite bio-oxidation can be divided into three phases according to the dynamic test of bio-oxidation of pyrite (100), (110) and (111). The first is an initial one of pyrite bio-oxidation named as pitting bio-oxidation. The second is of surface bio-oxidation and the third is that the pyrite crystal is seriously oxidized and corroded by bacterium and finally broken. The bio-oxidation intensity of pyrite crystal faces is ranked as (111)>(110)>(100).