Objectives:The Qinglong antimony deposit is hosted by the Dachang Layer which is dominated by silicified volcaniclastic rocks in Dachang district, southwestern Guizhou, SW China. In particular, the Dachang Layer is famous because of characteristic lithological composition and tectonic position, and contains gold, antimony, fluorite and pyrite, etc. Although many geologists have presented a majority of studies on genesis of the Dachang Layer, it is still hotly debated as regarding to formation and evolution of the Dachang Layer. Therefore, in this paper, we systematically describe petrography characteristics and elements geochemistry to reveal the ore- controlling mechanism of the Dachang Layer and identify the evolution. Methods:Petrography and elements geochemistry of the Dachang Layer were carried out in this paper. Results: Petrography indicates that the Dachang Layer is formed in a restricted shallow- marine environment. Emei flood basalt events, mafic volcanic eruptions and submarine hydrothermal venting activities in Middle—Late Permian (~260 Ma), are probably responsible for its forming material. Trace element geochemistry analysis indicates that submarine sedimentary exhalative can provides Sb, As, Au, Ag and Pb during syn- diagenetic stage, and formed the source- bed of Qinglong deposit. Conclusions:Ore elements (Sb, As, Au, Ag and Pb) were enriched in the Dachang Layer during syn- diagenetic stage.