<b><i>Introduction:</i></b> Hyperbaric oxygen (HBO) has been used for the treatment of cerebral palsy for more than 20 years, but its efficacy and safety are still controversial. In this systematic review and meta-analysis, we evaluated the currently promulgated data related to the efficacy of HBO for patients with cerebral palsy. <b><i>Methods:</i></b> We searched the PubMed/Medline, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure, and Wanfang databases (from their inception to April 2020) for randomized controlled trials published in English or Chinese. Two researchers used the Cochrane Collaboration tool for data extraction and an independent quality assessment. The extracted data were analyzed by Review Manager 5.3 software. <b><i>Results:</i></b> A total of 25 studies consistent with the inclusion criteria were included, with a total of 2,146 people, which included 1,185 participants in the HBO group and 961 in the control group. This meta-analysis showed that when compared with the controls, HBO therapy can improve the gross motor functions evaluated by the Gross Motor Function Measure (<i>n</i> = 696, SMD 0.29, 95% CI [0.07–0.51], Z = 2.62, <i>p</i> = 0.009) and Gross Motor Function Classification System (<i>n</i> = 248, MD –0.40, 95% CI [–0.52 to –0.27], Z = 6.28, <i>p</i> < 0.00001), global developmental level evaluated by Gesell (<i>n</i> = 560, RR 1.30, 95% CI [1.19–1.42], Z = 6.03, <i>p</i> < 0.00001) and developmental quotient (<i>n</i> = 374, MD 8.25, 95% CI [6.48–10.01], Z = 9.15, <i>p</i> < 0.00001) and language expression (<i>n</i> = 270, MD 4.34, 95% CI [2.30–6.38], Z = 4.17, <i>p</i> < 0.00001) and comprehension (<i>n</i> = 270, MD 4.87, 95% CI [2.87–6.88], Z = 4.76, <i>p</i> < 0.00001). HBO therapy only caused mild ear pain. However, the quality of the data for all outcomes evaluated by the Grading of Recommendations Assessment, Development, and Evaluation analysis was very low. <b><i>Conclusions:</i></b> HBO therapy may produce a much more efficient clinical experiment result than the control group with cerebral palsy patients, and HBO therapy is well tolerated and relatively safe for the included participants.