Objective:This study determined the clinical efficacy of extracorporeal shockwave therapy and the predictors of its efficacy for knee osteoarthritis.Data Sources:Electronic databases and search engines, namely MEDLINE, PubMed, EMBASE, Cochrane Library Database, Physiotherapy Evidence Database (PEDro), China Academic Journals Full-text Database, and Google Scholar, were searched until 5 March 2019, for randomized controlled trials without restrictions on language and publication year.Review Methods:Eligible trials and extracted data were identified by two independent investigators. The included articles were subjected to a meta-analysis and risk of bias assessment. Outcomes of interest included treatment success rate, pain, and physical function outcomes. A meta-regression analysis was performed to determine the predictors of treatment outcomes following shockwave therapy.Results:We included 50 trials (4844 patients) with a median (range) PEDro score of 6 (5–9). Meta-analyses results revealed an overall significant effect favoring shockwave therapy on the treatment success rate (odds ratio 3.22, 95% confidence interval (CI) 2.21–4.69, <i>P</i> < 0.00001; heterogeneity (<i>I</i><sup>2</sup>) = 62%), pain reduction (standardized mean difference (SMD) −2.02, 95% CI −2.38 to −1.67, <i>P</i> < 0.00001; <i>I</i><sup>2</sup> = 95%), and Western Ontario and McMaster Universities Osteoarthritis Index function outcome (SMD −2.71, 95% CI −3.50 to −1.92, <i>P</i> < 0.00001; <i>I</i><sup>2</sup> = 97%). Follow-up duration and energy flux density were independent significant predictors of shockwave efficacy.Conclusion:Shockwave therapy is beneficial for knee osteoarthritis. Shockwave dosage, particularly the energy level and intervention duration, may have different contributions to treatment efficacy.