Extracorporeal shockwave therapy (ESWT) has become a common practice for treating knee osteoarthritis (OA). However, the effectiveness and safety of this treatment are still questionable. This meta-analysis is aimed at determining the degree of pain reduction and functional outcome after ESWT for knee OA.We systematically searched MEDLINE, EMBASE, and other online databases. The articles comparing the outcomes between ESWT and controls were included in the analysis.Nine studies with 705 patients were included. The pooled data revealed significantly lower pain scores in the ESWT groups than in the control groups within two weeks of treatment and six months after treatment (visual analogue scale, - 1.59, p = 0.0003, 95% confidence interval (CI) - 2.45 to - 0.72 at 2 weeks; - 1.12, p = 0.005, 95% CI - 1.89 to - 0.34 at 6 months). The ESWT group also had better functional outcomes four to six weeks post treatment (Western Ontario and McMaster Universities Osteoarthritis Index, - 11.96, p = 0.003, 95% CI - 19.76 to - 4.15). No rebound pain was noted for up to 12 months.Using ESWT to treat knee OA may reduce pain and improve functional outcomes. The effect may last six months to one year. More prospective studies are needed to investigate the settings for ESWT to optimize treatment results.