[Objectives] The Forest Musk Deer (Moschus berezovskii) is a first-class nationally protected species in China. Due to human disturbance and habitat fragmentation, its wild population has been declining. Although this species is present in the Dalaoling National Nature Reserve, the research on M. berezovskii remains in its early stages, with a lack of in-depth studies on its activity rhythms and a comprehensive assessment of its population dynamics. This study aims to systematically analyze the activity patterns of M. berezovskii using infrared camera trap technology, assess the temporal overlap of its activity rhythms with those of five sympatric ungulate species, and also estimate its population density. [Methods] We deployed 763 infrared camera trap sites across the Dalaoling National Nature Reserve from June 2019 to October 2024, which resulted in 91 247 camera trap days (Fig. 1). A total of 68 616 independent events were recorded, including 481 valid independent photos of M. berezovskii. Activity rhythms were analyzed via kernel density estimation (KDE) to identify activity peaks. The temporal niche overlap coefficient (Δ) with sympatric ungulates was calculated, and the population density was estimated via the random encounter model (REM). In addition, t-tests were conducted to analyze differences in the monthly and seasonal activity intensity of M. berezovskii and compare diurnal activity indices across the 12 months. All data and statistical analyses were performed in R (version 4.3.0). [Results] During the monitoring period, a total of 68 616 independent events were recorded, yielding 481 valid independent photos of M. berezovskii, resulting in a relative abundance index (I_RA) of 2.15—the lowest among sympatric ungulate species in the Dalaoling National Nature Reserve. The daily activity pattern of M. berezovskii was clearly multimodal, with pronounced peaks at 17:00 ~ 18:00, 23:00 ~ 24:00, and around 03:00 (Fig. 3a). Coefficients of overlap analysis showed that its activity rhythm differed from those of all five sympatric ungulate species (Figs. 3b ~ f, P < 0.001):overlap was moderate with Chinese Serow (Capricornis milneedwardsii) and Wild Boar (Sus scrofa), but high with Tufted Deer (Elaphodus cephalophus), Chinese Goral (Naemorhedus griseus), and Reeves’s Muntjac (Muntiacus reevesi). Day-night rhythm analysis indicated significant monthly variation in the diurnality index β (Fig. 4, x² =54.03, df = 11, P < 0.001). The species was diurnal in August and October (β > 0.54) and nocturnal in all other months (β < 0.54). Activity intensity differed across months (Fig. 5, G = 80.45, df = 11, P < 0.001) and seasons (G = 61.82, df = 3, P < 0.001). The species exhibited the highest overall activity in winter with a pronounced peak in November. The intensity declined gradually through spring, rose modestly in June, and remained low from August to October. Daily activity rhythms showed no significant difference between spring and summer or between summer and winter, whereas all other seasonal comparisons revealed significant variations (Fig. 6, P < 0.05). Application of the REM placed the Moschus berezovskii population in Dalaoling National Nature Reserve at 0.11 ~ 0.17 ind/km², with the 2020 estimate representing the lowest density recorded during the study period (Table 2). [Conclusion] For the first time, this study systematically analyzes the activity rhythms and population density of M. berezovskii in the Dalaoling area. The results reveal significant temporal niche differences in activity rhythms between M. berezovskii and other ungulate species in the region. These findings enhance our understanding of the activity mechanisms of M. berezovskii in Dalaoling and provide a foundational reference for future monitoring and management efforts in the reserve.