In the present paper, the natural pyrite was the sample. With the UV-visible near-infrared spectrophotometer Cary 500, we measured the absorption and reflection spectra of the sample within 200～2 000 nm range, calculated the absorption coefficient and figured out the forbidden band of the sample according to the Tauc regulation. The authors discovered that the light absorption coefficient of natural pyrite measured is 105 order of magnitude; in the absorption pattern we found obvious shoulder line structure and we can judge that the sample belongs to indirect forbidden band semiconductor, its forbidden band was 0.64 eV in width and the “limit conversion efficiency” corresponding to 0.64 eV could reach 14% or so. With the comparison of the results of this paper and the forbidden band of the solar battery materials at present in common, this paper mainly analyzed the effect of the light absorption coefficient and forbidden band on the photoelectric conversion efficiency of pyrite. The authors found that its high absorption coefficient provided the possibility that pyrite will be used as solar battery with the film form, but its forbidden band was narrower than the theoretical number. The authors could broaden its forbidden band or make composite films to use.