Objective To investigate gait characteristics of older adults during stair ascent and descent, and mechanical properties of lower extremity joint movement. Methods A total of 17 young adults and 15 old adults were required to ascend and descend a five-step staircase at natural walking speed. The gait parameters, lower limb joint angles and ground reaction force were obtained using infrared high speed motion capture system and three-dimensional force platform, the joint moments and powers were calculated by inverse dynamics approach, and the influence of age on those parameters was analyzed by independent samples t-test. Results Compared with young adults, older adults had a relatively longer gait cycle, as well as an obviously lower walking speed and frequency during stair ascent and decent (P<0.05). Meanwhile, the support phase and swing phase in older adults during stair ascent and decent were obviously prolonged and shortened respectively (P<0.05). The change trend for joint angle, moment and power of lower limbs during stair ascent and decent was consistent in both young and older adults. However, during stair ascent, older adults were mainly maintained by the generation of ankle and knee joint power, while young adults were mainly maintained by the energy at the proximal limb, especially more knee power was used. For older and young adults, energy absorption during stair decent played an important role in knee joints. Conclusions With aging, lower limb function and muscle strength will decrease. Older adults are afraid of falling down during stair ascent and decent, and try to compensate for the instability of the body by reducing swinging time. The research findings provide references for rehabilitation management and functional assessment on fall prediction of older patient populations in clinical practice.