[Objectives] This study aimed to elucidate the sympatric coexistence mechanism of Red Deer (Cervus elaphus), Wild Boar (Sus scrofa), and Asian Badger (Meles leucurus) through temporal niche differentiation via resource utilization and time allocation in the Hanshan National Nature Reserve, Inner Mongolia, China. We specifically investigated how fine-scale partitioning of daily and seasonal activity rhythms minimizes temporal niche overlap under varying environmental conditions (e.g., temperature and resource availability), thereby reducing potential interspecific competition for shared resources in their overlapping habitats. [Methods] From July 2023 to July 2024, 58 passive infrared cameras (“Huangyezhi Eye ST1”) were deployed across a series of standardized 1 km × 1 km grid units within the reserve. Cameras were strategically placed at a height of (60 ± 10) cm above ground in representative habitats, including 29 cameras in forest, 23 cameras in grassland/forest-grassland, and 6 cameras in ecotone, prioritizing areas of high animal activity (such as trails and water sources within a radius of 200 m). This resulted in a total of 21 113 effective camera-days and 4 183 independent valid photos. The species-specific valid photos included 1 759 for Red Deer, 848 for Wild Boar, and 819 for Asian Badger. The monthly relative abundance index (I_MRA) was calculated as follows:I_MRA = M_ij/T_i, where M_ij is the number of independent valid photos of species j in month i, and T_i is the total number of camera-days for month i across all sites. In order to study the daily activity rhythms, we adopted the kernel density estimation (KDE) to model 24-h activity patterns and quantify the coefficient of overlap (Δ, ranging from 0 to 1, where 0 indicates no overlap and 1 indicates complete overlap) between species pairs by the overlap package in RStudio (V. 4.4.0). Seasonal comparisons (Spring, March to May; Summer, June to August; Autumn, September to November; and Winter, December to February) were conducted. The significance of differences in coefficient of overlap was assessed by Wald tests (1 000 bootstrap iterations) via the compareCkern function. Peak activity time and core activity windows were identified from KDE curves. [Results] (1)Red Deer and Asian Badger exhibited bimodal monthly activity patterns, with peak I_MRA values (> 0.50) observed in late spring and early summer (May to June) and autumn (September) (Fig. 2). Wild Boar displayed a unimodal pattern, exhibiting a pronounced peak in spring (May) with peak I_MRA greater than 0.50 (Fig. 2). Spatial overlap across all seasons was near-complete (98.3% ~ 100% co-occurrence at camera sites, Table 1), with no significant spatial niche differentiation among the three species. (2) Daily activity patterns showed significant temporal partitioning. Red Deer (bimodal, peaks 03:00 ~ 05:00 and 18:00 ~ 20:00) and Asian Badger (bimodal, peaks 03:00 ~ 05:00 and 18:00) had high overlap (Δ = 0.816 2, P < 0.05), achieving segregation primarily by a 1-h shift in the evening peak (18:00 vs. 19:00) (Figs. 3a, c). Wild Boar exhibited a diurnal-evening bimodal activity pattern, with its main diurnal activity peak (08:00 ~ 10:00) significantly segregated from the crepuscular peaks of the other two species, and only partial overlap with Red Deer and Asian Badger at the secondary evening peak at 18:00. It showed low temporal overlap with Red Deer (Δ = 0.659 8, P < 0.05) and Asian Badger (Δ = 0.616 4, P < 0.05) (Figs. 3b, c). (3) The activity rhythm overlaps between Red Deer and Asian Badger was the highest in spring (Δ = 0.817 3, P < 0.01; concurrent peaks 03:00 ~ 05:00, Fig. 4a). The most significant niche segregation between Red Deer and Wild Boar was observed in summer (Δ = 0.343 7, P < 0.01, Fig. 6), and the most significant niche segregation between Wild Boar and Asian Badger was observed in winter (Δ = 0.273 9, P < 0.01, Fig. 5). [Conclusion] This study demonstrates that the Red Deer, Wild Boar, and Asian Badger achieve sympatric coexistence in the Hanshan National Nature Reserve through significant temporal niche differentiation. Key mechanisms include fine-scale shifts in daily activity peaks (e.g., 1-h crepuscular offset between Red Deer and Asian Badger and diurnal-crepuscular peak segregation by Wild Boar) and pronounced seasonal adjustments in activity timing. These dynamic behavioral adaptations minimize temporal niche overlap, and the species dynamically respond to seasonal resource fluctuations (temperature and food availability) and breeding needs to support sympatric coexistence. The temporal niche differentiation pattern (e.g., activity peak dislocation, seasonal overlap variation) of the three species is an important behavioral strategy for their sympatric coexistence. This finding provides a scientific basis for biodiversity management (e.g., spatiotemporal allocation of key resources) and climate change response strategy formulation in Hanshan National Nature Reserve.