Objectives: This article mainly discusses the depositional environment, provenance characteristics and sedimentary tectonic background of the Longmaxi Fm mudstone in the Yingjing area, southwestern margin of the Sichuan Basin. The correspondence relationship between mudstone and source rocks was initially established to support the related basic geological research of regional shale gas exploration and development.Methods:The detailed geological survey and systematic research on petrology, mineralogy, element geochemistry were used to study the Longmaxi Formation.Results: The content of sandstone and calcareous of the Longmaxi Fm is relatively high, This indicates a shallow water deposition environment.The characteristics of REE and A-CN-K diagram show the mudstone of the Longmaxi Fm is less affected by diagenesis and metasomatism.The high content of K2O, Rb and Al2O3/TiO2and the negative δEuN indicate that the source rocks are feldspathic igneous rocks and granite. The ICV> 1, CIA=66, Th/U is similar to the UCC value, Rb/Sr is significantly lower than PAAS, indicating that its source is the rapid deposition product of the first cycle of the near source. La/Yb、LREE/HREE and Sc/Cr were similar to those of passive continental margin.Conclusions:Affected by tectonic uplift, the entire Longmaxi Fm in the study area was a shallow-water continental shelf sediment,and the sedimentary background was mainly the passive continental marginal environment. The source rocks was mainly provided by the early Neoproterozoic platform cover of Kangtien old land on the west side.The paleoclimate of the provenance was cold and dry, and experienced low-level chemical weathering.