Abstract: Lailishan tin deposit, located in the eastern of Himalayas -Tethys tectonic domain and the western margin of the southern section of Sanjiang tectonic belt, is one of the most famous tin polymetallic deposits in western Yunnan. To investigate its ore genesis and provide scientific basis for the exploration and prospecting, the authors studied typomorphic characteristics of pyrite in the mining area. A large number of pyrite grew within the mineralization stages of the Lailishan tin deposit. The authors researched the infrared spectrum of pyrite through Fourier transform infrared spectrometer. The analysis results show that there were isomorphism substitutions of pyrite at different degrees and the difference between spectrogram and absorbancy of pyrite at different mineralization stages, and also show the characteristic peak shifting towards short wave from the first stage to the fourth stage. And the absorbance ratios of pyrite display the regular changes at different mineralization stages. The results above have some guiding significance for further prospecting in this area.