BACKGROUND: De Qi is a special sensational response upon acupuncture needling. According to traditional acupuncture theory, the treatment is "effective only after Qi arrival"; that is, De Qi is an important indicator of therapeutic efficacy and good prognosis. However, it is still disputable whether De Qi improves the efficacy of acupuncture therapy. This prospective, randomized controlled trial aims to explore the influence of De Qi induced by acupuncture on immediate and accumulated analgesic effects in patients with knee osteoarthritis (KOA). METHODS/DESIGN: Eighty-eight patients with KOA will be recruited and randomly assigned to the De Qi group (enhanced stimulation to evoke De Qi) and the control group (weak stimulation to avoid De Qi) in the Department of Acupuncture and Physical Therapy, Beijing Luhe Hospital Affiliated to Capital Medical University. Each patient will receive three 30-minute sessions per week for 4 consecutive weeks and undergo a 1 month follow-up. The severity of knee pain, as measured on a 100-mm visual analog scale (where 0 indicates no pain and 100 indicates intolerable pain) will be used as the primary outcome, and the Knee injury and Osteoarthritis Outcome Score will be used as the secondary outcome. Both indexes will be measured before and after the 1 (for evaluating the immediate analgesic effects), 3, 6, 9, and 12 (for evaluating the accumulated analgesic effects) treatments and at the end of the follow-up. The intensity of the De Qi sensation will be assessed by the Chinese-Modified Massachusetts General Hospital Acupuncture Sensation Scale at the end of each treatment. Side effects during the treatments will be recorded and analyzed as well. The comparisons between the De Qi group and the control group will be done by using both an intention-to-treat analysis and a per-protocol analysis. DISCUSSION: This prospective randomized controlled study will be helpful in enhancing our understanding of the analgesic effect of De Qi on patients with KOA and may provide a clinical basis for further investigation of the relationship between De Qi and the therapeutic efficacy of acupuncture, thereby offering some evidence for the role of De Qi in an efficacious acupuncture therapy. TRIAL REGISTRATION: Chinese Clinical Trial Registry, ChiCTR-IIR-16008972 . Registered on 4 August 2016 Additional file 2.