Abstract: The comparative study of sympatric species is helpful for further analysis of interspecies behavior, ecological adaptation and co-existence mechanism. In order to explore the differences in daily activity pattern, temporal niche differentiation and coexisting mechanism of sympatric species, infrared camera were used to continuously monitor Sambar (Cervus equinus) and Tufted Deer (Elaphodus cephalophus) from May 2017 to April 2018 in Gongga Mountain National Nature Reserve, Sichuan province. The kernel density estimation and coefficient of overlap were used to analyze the daily activity rhythm of the two species. The results showed that both Sambar (Cervus equinus) and Tufted Deer (Elaphodus cephalophus) were more inclined to the morning and dusk activity, but the similarity of the daily activity rhythm between the two was lower (Δ=0.80, P<0.01). There were three activity peaks in the daily activity rhythm of Sambar, which were 03:30—04:00, 06:00—08:00 and 18:00—23:30, while there were only two activity peaks in the daily activity rhythm of Tufted Deer, which were 07:00—12:00 and 17:00—21:30. The morning activity peak of Sambar was significantly earlier than that of Tufted Deer, while the end time of dusk activity peak was 2 hours later. The daily activity rhythm of the two species was significantly different between seasons (Sambar: Δ=0.93, P=0.03; Tufted Deer: Δ=0.88, P<0.01). The morning activity peak of the two species appeared half an hour later in the dry season than that in the rainy season, while the dusk activity peak (19:00) of Tufted Deer was one hour earlier than that in the rainy season (20:00). Compared with the rainy season, the dusk activity peak values of both were larger and the activity peaks of both were longer in the dry season than that in the rainy season, however, in the rainy season, the activity peak values and activity peaks of the two species showed opposite trend. The overlap index of the daily activity rhythm between Sambar and Tufted Deer during the research period was lower (Δ=0.80), and the overlap index (Δ=0.83) and the maximum activity peak value (0.12) in the dry season were higher than those in the rainy season (Δ=0.74; the peak value was 0.10), but there were significant differences between the whole and the seasons (P<0.01). This study showed that sympatric species of Sambar and Tufted Deer could coexist through temporal niche differentiation to reduce competition for food, space and time resources. The results of this study can provide important data reference for further research on the co-existence mechanism of sympatric species and for the formulation of targeted conservation and management strategies.