The black rock series explosion in the early Cambrian is of great geological significance for understanding the Earth’s paleomarine environment. In this paper, the source, genesis and sedimentary environment of the black rock series of the Shuigoukou Formation in the Xichuan- Neixiang area of South Qinling were studied by detailed profile measurement, thin section identification, electron probe, and measurement of major and trace elements. The results show the black rock series have typical microcrystalline quartz structure of marine siliceous rocks.The black rock series may have been affected by biological and hydrothermal processes because of the presence of fluorite, pyrite, barite, and apatite identified by electron probe. Combined with the discriminant diagram of siliceous sources, the results indicate that the siliceous sources are mainly biogenic and contain a small amount of hydrothermal silicon. The rare- earth element (REEs), redox sensitive elements and the discriminative diagrams of genesis and tectonic background of the black rock series suggested that they were mainly deposited in anoxic- reductive continental margin- deep sea basin stagnant hydrostatic environment. Seawater was mixed with nutrient enriched submarine hydrothermal fluid and subsequently driven by upwelling towards the continental margin far away from hydrothermal activity center. As a result, SiO2 within the regional seawater became over- saturated and thus precipitated. This study suggests that the special marine environment and ecosystem of the early Cambrian promotes the chemical precipitation of silica colloidal particles,and the metabolic activity of microorganisms played an important role in this process.