Abstract: Cymbellaceae and Gomphonemataceae were established in 1833 by Greville and 1844 by Kützing, respectively. But in preliminary study, both families were put into Diatomaceae by Smith 1872 or into Naviculaceae (subfamily Gomphocymbelloideae) by Hustedt 1930. Until 1960―1970s, Patrick & Reimer gave these two families the same status as Naviculaceae, belong to Biraphidinales. Round, et al. established a new order – Cymbellales in 1990, based on the structure of diatom valves in SEM, including Rhoicospheniaceae, Anomoeoneidaceae, Cymbellaceae and Gomphonemataceae. Cymbellaceae include: Placoneis Mereschkowsky, Cymbella Agardh, Brebissonia Grun., Encyonema Kützing and Gomphocymbella Müller. Krammer seperated Cymbopleura subgenus from Cymbella, Cymbopleura (Krammer) Krammer were established in 1999. Gomphonema Ehrenb., Didymosphenia Schmidt, Gomphoneis Cl., Reimeria Kociolek & Stoermer and Gomphopleura Reichelt & Tempère belonged to Gomphonemataceae. Great Xing’an Mts. locats in northeast of China with a large area of wetland. During the investigation of diatoms from Great Xing’an Mts., species that belonged to Cymbellaceae and Gomphonemataceae preferred habitats with pH values ranging from 6 to 9. In total, we observed that 5 genera and 44 taxa belong to Cymbellaceae and 4 genera and 24 taxa belong to Gomphonemataceae. The Chinese name for Placoneis was firstly used among these genera. The detailed description for the genera Placoneis Mereschkowsky, Encyonema Kützing and Cymbopleura (Krammer) Krammer were given. For many years, Placoneis was within Navicula sect - Lineolatae, but it is much closely related to Cymbella and Gomphonema with a single, large elaborate plastid which is divided into two X-shaped plates lying against each valve, connected by a broad column which contains a large flat pyrenoid; Striae uniseriate, containing small round poroids closed by volate occlusions; Internal central raphe endings hooked towards the primary side of the valve; External central endings slightly expanded; External polar endings hooked towards the same or opposite sides. Encyonema and Cymbopleura share some features with Cymbella as cells dorsiventral, valves asymmetrical along the apical plane etc., but Encyonema was seperated from Cymbella by its raphe system parallel to ventral margin, terminal fissures curved towards ventral margin and without apical pore field. Cymbopleura was seperated from Encyonema and Cymbella because its terminal fissures are dorsally deflected, without stigmata, stigmoids and apical pore fields. In this paper, 15 taxa were reported as newly recorded species in China. They are Placoneis explanata (Hust.) Lange-Bertalot, Placoneis interglacialis (Hust.) Cox, Cymbella subarctica Krammer, Cymbopleura florentina (Grun.) Krammer, Cymbopleura neoheteropleura Krammer, Cymbopleura subcuspidata (Krammer) Krammer, Cymbopleura subrostrata (Cl.) Krammer, Encyonema elginense (Krammer) Mann, Gomphonema anglicum Ehrenb., Gomphonema distans (Cl.-Eul.) Lange-Bertalot & Reichardt, Gomphonema khentiiense Metzeltin, Lange-Bertalot & Nergui, Gomphonema liyanlingae Metzeltin & Lange-Bertalot, Gomphonema pala Reichardt, Gomphonema pseudopusillum Reichardt, Gomphonema sagitta Schumann. The morphological differences with other similar species are given. The habitats of these taxa in Great Xing’an Mts. and around the world were also discussed.