Many dispersed elements (such as Cd, Ge, Se, In and Ga, etc.) are enrichment in the sulfides of the Pb-Zn metallogenetic area in the northwest of Guizhou Province, China. In this paper, the occurrence states, regularities and mechanism of dispersed element Cd were studied by using the Electron Probe Microanalysis (EPMA) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), which shows that the Cd is in the form of isomorphism occurring in the sulfide phase mainly, especially the sphalerite and the accumulation regularities of Cd being the highest in sphalerite, followed by galena, and pyrite being the minimum. These features indicate that the Fe could be replaced by Cd in sphalerite, which is the result of “fluids-mixing”, maybe representing a new ore-forming mechanism.