Pyrite is one of the common natural mineral. It is easily oxidized and brings heavy metal contaminations, therefore it is the main source of acidity mine drainage. The study on the dynamics of pyrite is helpful to comprehending the mechanism of its pollution. In the present paper, an experimental method was designed that phenanthroline reacts with Fe2+ that is released from pyrite in solution, and produces stable orange-red complex compound. It can be detected by absorption spectroscopy. In-situ characterization of oxidation of pyrite can be achieved by this method. The results showed that the method is reliable and accurate, and it has high sensitivity and little interference; the reaction rate of oxidation increased linearly with time, corresponding to the characterization of zero-order reaction; oxidation of pyrite belongs to the surface reaction and the process of surface reaction is rate determining step.