Objective To observe the effects of electro-acupuncture on the joint loading during stair climbing in knee osteoarthritis (KOA) and explore the related biomechanical mechanism. Method Forty patients with KOA were randomly assigned to 20 patients in the observation group (electro-acupuncture group, EA group) and 20 patients in the control group (superficial acupuncture group, SA group), finally 18 patients in each group completed the study. The observation group chose seven knee acupuncture points and connected with electro-acupuncture instrument to take 2Hz square wave; while in the control group, the electro-acupuncture instrument was connected but not electrified after superficial acupuncture at non-acupoint points. Both groups consisted of 11 sessions of treatment in 3 weeks and 30 minutes per session. The three-dimensional gait analysis system was used to assess the ground reaction force during climbing stairs before and after treatment, biomechanical parameters included 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 ascending stairs and PFz of the left foot during descending stairs increased (P < 0.05); IFz of both feet during ascending stairs and IFz of the right foot during descending stairs significantly decreased (P < 0.05); no significant difference showed in SI% (P > 0.05). In SA group, only SI% of impulse increased (P < 0.05). There was no significant difference between two groups before and after treatment (P > 0.05). Conclusion Electro-acupuncture can effectively improve the joint load capacity and reduce the dynamic cumulative load during stair climbing in KOA, which may be helpful to slow down the course of disease.