As a crucial component of ecosystems, mammals serve as a key taxa indicator for biodiversity conservation management and assessment. Heilongjiang Liangshui National Nature Reserve is a critical habitat for wild mammals. To investigate the current status and temporal trend of mammal diversity in the region, from January 2018 to December 2021 and from April 2022 to December 2023, camera trapping was employed to track changes in mammal diversity in Heilongjiang Liangshui National Nature Reserve and 50405 capture dates and 5981 effective photographs were collected. The results are as following: 1. A total of 15 mammal species were recorded, belonging to 10 families and 5 orders. The sable (Martes zibellina) is classified as category I state key protected wild animal, and four species were classified as category II state key protected wild animals, including the yellow-throated marten (M. flavigula), leopard cat (Prionailurus bengalensis), Eurasian lynx (Lynx lynx), and Asian black bear (Ursus thibetanus). 2. The five most populous species in Liangshui National Nature Reserve were the roe deer (Capriolus pygargus) at 7.694, wild boar (Sus scrofa) at 1.458, Asian badger (Meles leucurus) at 0.809, Eurasian red squirrel (Sciurus vulgaris) at 0.650, and sable at 0.564. 3.The northern red-backed vole (Myodes rutilus) and striped field mouse (Apodemus agrarius) were only detected in 2022, while the Eurasian lynx was recorded in 2023 again after several years. 4. According to EstimateS9.1, the number of species actually monitored constituted an estimated 75% to 83.33% of the total mammal species. 5. There was an increasing trend in the number of species with the highest number being 14 species in 2022. The annual diversity index showed great fluctuations ranging from 0.833 to 1.394 without significantly interannual differences (χ²=7.496,df=5,P>0.05). However, the evenness index showed significant interannual differences with a decreasing trend (χ²=11.525,df=5,P<0.05). The lowest values for both the diversity index and the evenness index were observed in 2021, at 0.833 and 0.428, respectively. Surveying species diversity data serves as the foundation for biodiversity conservation management and assessment efforts. The research elucidates the current status and interannual variations of mammalian diversity in Heilongjiang Liangshui National Nature Reserve, provides reasonable suggestions on the effective conservation and management of mammal diversity and a scientific foundation for conserving rare mammals and their habitats.