Objective To observe the effects of electro-acupuncture on loading of lower limb joints in patients with knee osteoarthritis (KOA) during stair climbing and explore the related biomechanical mechanism. Methods Forty patients with KOA were randomly assigned, with 20 patients in observation group (electro-acupuncture group, EA group) and 20 patients in control group (superficial acupuncture group, SA group). Finally 18 patients in each group completed the study. In observation group, seven knee acupuncture points were chosen and patients were connected with electro-acupuncture instrument; while in control group, the electro-acupuncture instrument was connected but not electrified after superficial acupuncture at non-acupoint points. The three-dimensional gait analysis system was used to assess the biomechanical characteristics during stair climbing before and after treatment, including peak vertical force (PFz), vertical impulse (IFz) and symmetry index (SI%). Results After 3 weeks of treatment in EA group, PFz of the right foot during stair ascent and PFz of the left foot during stair descent increased (P＜0.05); IFz of both feet during stair ascent and IFz of the right foot during stairs descent significantly decreased (P＜0.05); no significant differences were found in SI% of peak and impulse (P＞0.05). In SA group, only SI of impulse during stairs ascent increased (P＜0.05). There was no significant difference between two groups before and after treatment (P＞0.05). Conclusions Electro-acupuncture can effectively improve the joint load capacity and reduce the dynamic cumulative load of patients w