Abstract: In order to investigate the fauna and diversity of small mammals in Baishuihe National Nature Reserve Nature Reserve, a survey of small mammals was conducted by snap traps and pitfall traps from April to September 2020. The survey covered 10 survey quadrats at 8 elevation sections, spanning from 1400 m to 3350 m altitude, and 26 species of small mammals were collected. According to the historical records and published literatures published by the project team, a total of 44 species of small mammals belonging to 4 orders and 13 families were identified in Baishuihe National Nature Reserve. Among them, there were 23 species of Rodentia, 12 species of Insectivora, 5 species of Chiroptera and 5 species of Lagomorpha. According to the calculation of biodiversity index, Margalef index and Shannon-Weiner index showed the lowest species diversity at 1400 m altitude, Simpson index showed the lowest species diversity at 3550 m altitude, species evenness index showed that the relative density of species at 1500 m was the most uneven, and the number of individuals at 1800 m was the most uniform. The conclusion of this study could provide theoretical and data support for species diversity research and biological protection of small mammals in Baishuihe National Nature Reserve.