Objective To obtain the statistical data from the range of motion in lower limb of the Chinese people during their stair ascent so as to provide references for the design of artificial joints with large range flexion. Methods Common staircase as an experimental device was designed, and motion capture system（Optotrak Certus, NDI）and 3D force plate（AMTI, Bertec）were used to establish a systematic method to measure the lower limb motion from 40 subjects during stair ascent. Results The variation of joint angle and range of motion in hip, knee and ankle joints for the 40 subjects in different directions within one cycle were obtained and calculated. The range of motion in hip, knee and ankle joints at the sagittal plane were -1.6°~66.7°, 0°~91.4°,-20.8°~22.4°, respectively. Conclusions During the movement of stair ascent, the range of motion at the sagittal plane in hip, knee and ankle joints reached the maximum, with the most flexion in hip and knee. Compared with the movement during walking and jogging on flat road, the range of motion in joints both in hip and knee at the sagittal plane were larger during stair ascent.