INTRODUCTION: Pulsed electromagnetic field (PEMF) is an available treatment for knee osteoarthritis (KOA), which is the most common cause of pain and disability. Nonetheless, whether the clinical effects are like that of most used drugs is unclear. Thus, this study aims to determine the effect of PEMF on pain relief by comparing them with the positive drug (celecoxib). Furthermore, this clinical trial aims to evaluate the effect of PEMF on function and quality of life with a long-term follow-up. METHODS AND ANALYSIS: This two-armed, non-inferiority, randomised, controlled trial will be conducted in the outpatient physiatry/physiotherapy clinic or inpatient ward of 17 hospitals in China. A total of 428 individuals will be included who are more than 40 years of age with diagnosed KOA. The participants will be randomly allocated to the PEMF group: receiving a 6-week PEMF (15 Hz, 30 mT) at a frequency of 40 min per day, 5 days per week plus sham drug (n=214), or drug group: receiving a 6-week celecoxib 200 mg combined with sham PEMF (n=214). Clinical outcomes will be measured at baseline (T0), mid-term of intervention (T1), post-intervention (T2), 10, 18 and 30 weeks (T3-5) of follow-up after randomisation. The primary outcome will be the Western Ontario and McMaster Universities (WOMAC) pain index. The secondary outcomes will be WOMAC function and stiffness, pain measured by numerical rating score, quality of life, 6-minute walk test, pain catastrophising scale and responder index. ETHICS AND DISSEMINATION: The trial is performed following the Declaration of Helsinki. The study protocol and consent form have been approved by the Ethics Committee on Biomedical Research of West China Hospital of Sichuan University (#2021-220). All patients will give informed consent before participation and the trial is initiated after approval. Results of this trial will be disseminated through publication in peer-reviewed journals. TRIAL REGISTRATION NUMBER: ChiCTR2100052131.