Abstract: Activity rhythm is a dynamic life strategy of animal endogenous rhythm in response to environmental stress, which reflects the individual's adaptation to resources and threats. Tufted deer (Elaphodus cephalophus) is the dominant ungulate species widely distributed in southwest mountain forests of China, but no special reports have been published on it so far. From January 2017 to November 2019, infrared cameras were used to investigate the Tufted deers in Baihe National Nature Reserve in Sichuan province, in order to reveal their activity rhythm and seasonal changes. The results showed that: 1) Tufted deer had obvious typical dawn and dusk activity, with the highest activity intensity from 6:00 to 10:00 and from 16:00 to 20:00 respectively. 2) The seasonal changes of activity rhythm was apparent, with the highest overlapping index in spring and summer ( \widehat\Delta =0.90 ) and the lowest overlapping index in autumn and winter ( \widehat\Delta =0.78 ). Compared with summer and autumn, the activity peak in the morning was delayed and the activity peak in the evening was advanced in spring and winter. 3) Tufted deer had no obvious nocturnal activity, but the nocturnal activity in winter and spring was obviously higher than that in summer and autumn. We believed that extreme temperature and food supply were the main drivers of seasonal variations of their daily activity rhythms.