In July 2015, samples of epilithic diatom collected from Lake Selincuo in Tibet Autonomous Region, China were observed and identified. Three speices belonging to the genus of Brachysira were found. Brachysira aponina (Kützing)is a newly recorded taxon in China. The others were B. microcephala (Grunow) Compère and B. vitrea (Grunow) Ross. The characteristics of B. aponina were described in details and the ultrastructure of two types of B. microcephala and B. vitrea were redescribed by observation of light microscope (LM) and scanning electron microscope (SEM). B. aponina is characterized by narrow round ends, small or round center area and straight axial area with siliceous longitudinal ribs. Raphe is simple with M-shaped distal ends. The main features of B. microcephala type 1 are subcapitate ends, asymmetrical-round area and T-shaped distal ends. B. microcephala type 2 is characterized by capitate ends. The striae are radiate at valve center,but parallel towards the ends. B. vitrea mainly has elliptic-lanceolate valve with elongate and capitate ends,small and ovate center area and "T"-shaped distal ends. In addition, characteristics between the 3 species and other resembling gomphonemoid species of Brachysira were compared and discussed. Meanwhile, the ecology and distribution of the three species were also described in detail.