Pyrrhotite from Dingjiashan Pb-Zn ore district is investigated by means of optical microscope, X-Ray diffraction, micro-area chemical analysis, field observation and mineralogical mapping. The result suggests that the ore-forming process of Dingjiashan Pb-Zn ore district is resulted from the contact metasomatism between Yanshanian granite and the regional metamorphosed calcareous rock of mesoproterozoic-neoproterozoic Mamianshan Formation.