A new microfossil assemblage was discovered from the Dengying Formation, Upper Sinian of the Wuhe section, Taijiang County, Guizhou Province, with a cone- and tube-shaped and 30～70 μm long. They were considered as Carinchitiids, Hexangulaconulariids and Punctatus. Furthermore, a new microfossil taxon with cone-tube and thin shell, was discovered from the upper dolomites of Dengying Formation. It was Spondylotubus taijiangensis Yang(gen. et sp. nov.). Based on the discoveries, it was suggested that the Precambrian-Cambrian boundary would be located at the base of upper dolomites of the Dengying Formation, which was concord with the boundary of Precambrian-Cambrian in Yunnan, Sichuan and Shaanxi Provinces. The microfossils from Late Sinian Dengying Formation in Guizhou were similar to small shall skeletal in morphology, but size of the microfossils were smaller than that of small shall skeletal in early Cambrian. The microfossils might indicate an inhabiting taxa in deeper shelf. This discovery was helpful to study on early Cambrian evolution of metazoan, and the boundary of Precambrian-Cambrian.