Objective: To systematically review the efficacy of hydrotherapy in patients with mild-to-moderate Parkinson’s disease (PD). Methods: To obtain data of randomized controlled trials (RCTs) which studied the efficacy of hydrotherapy for PD, we searched Web of Science, PubMed, EMbase, The Cochrane Library, Ovid, CNKI databases, WanFang Data and VIP Database for Chinese Technical Periodicals from databases inception to March 1st, 2019. Literature screening, data extraction, and the risk of bias assessment for all eligible studies were conducted by two researchers independently. Meta-analysis was performed using RevMan 5.3 software. Results: Our search identified 233 articles, of which 11 RCTs with a total of 328 patients were included for analysis. Results showed that hydrotherapy could significantly improve balance ability (MD=3.12, 95% CI: 1.34 to 4.89, P=0.0006), functional mobility (MD=–1.36, 95% CI: –1.96 to –0.76, P<0.00001), release pain (MD=–1.20, 95% CI: –1.81 to –0.59, P=0.0001), and quality of life (MD=–6.35, 95% CI: –12.17 to –0.54, P=0.03) of mild-to-moderate PD patients. However, there was no statistically significant difference between two groups on motor function, exercise tolerance and freezing of gait (all P values >0.05). Conclusion: Hydrotherapy is efficacious in improving mild-to-moderate PD patients’ balance ability, functional mobility, quality of life, and releasing pain. Because of the limitation of quantity and quality of included studies, more high-quality studies are needed to verify the above conclusion.