The current paper carried out a study on the morphological characters of Distrionella incognita (Reichardt) D.M. Williams collected from a river in Menyuan County of Qinghai Province, using light and scanning electron microscope. In order to determine its taxonomic genus and species, the characteristics of the species are compared with its similar species, D. asterionelloides D.M. Williams. The results demonstrate that, (1) the specimens of D. incognita collected from Menyuan County of Qinghai Province have eight diagnostic characters: ① narrowlanceolate valve outline and capitate apices; ② three types of transapical ribs: primary rib, secondary rib, and tertiary rib; ③ stellate colony; ④ unevenly distributed uniseriate striae on the valve surface; ⑤ not raised sternum; ⑥ each valve bearing only one rimoportula at one apex; ⑦ nonocellulimbustype apical pore field; ⑧ only one row of poroids along the midline of the valvocopula. Therefore, it is confirmed as determined that the diatom is D. incognita in this paper. (2) To characterize D. incognita, a comparison was made with its similar taxa, D. asterionelloides. The main difference between the two species is that the former can form a zigzag or stellate colony, while the latter is solitary and does not form a colony. Thus, the two species are different. (3) The results of this study expanded the geographical distribution area of D. incognita, confirmed that D. incognita is a new record species in China. The permanent slides are deposited in the Herbarium of Jishou University (JIU).