The Balang Formation in Geyi section, Taijiang County, Guizhou Province, exposed completely and contained abundant fossils. The Balang Fauna which yielded in the middle—upper parts of the Balang Formation in Geyi section is diverse in composition. Therefore the section is an important locality of the Balang Fauna. Based on detailed investigation of field work, the characteristics of fossil preservation in different beds and analysis of thin section of rock samples from Geyi section, writers synthesized these data to analyze sedimentary characteristics and sealevel changes of the Balang Formation in Geyi. The conclusion was that the Balang Formation in Geyi was deposited in an environment of deepwater shelf under normal salinity. Organisms lived in an oxidizing environment—lowoxidizing environment and beds which contained abundant fossils undergone rapid deposition events. In general, seawater depth changed from deep to shallow during the deposition period of Balang Formation, including two obvious wave influences, which seawater depth deepened firstly then shallowed and the reduction—oxidation interface changed on seafloor.