Background: M6A methylation modification of RNA can regulate the development of tumor cells. METTL3 is one of the modified methyltransferases. A growing number of studies have shown that high expression of METTL3 may be associated with the unfavorable prognosis in cancer patients and may become a new biomarker. Therefore, this meta-analysis was used to evaluate the prognostic value of METTL3 in cancer patients through the available literature information.Methods: Relevant studies were retrieved from electronic literature databases including six English databases and three Chinese databases. Correlation analysis was conducted by Stata SE 15.1 and RevMan 5.3 software. We analyzed 11 eligible studies with a total of 1638 cancer patients in this meta-analysis. We took advantage of HRs and ORs with 95% confidence intervals to evaluate the prognostic value of METTL3 in tumors. Besides,the article was qualified by MOOSE check lists and PRISMA Checklist. Results: The results of the meta-analysis indicated that high expression of METTL3 was associated with low overall survival (OS) (HR=2.67, 95%CI:2.19-3.25, P<0.00001) and disease-free survival (DFS) (HR=2.23, 95%CI:1.60-3.11, P<0.00001) in various cancers.Stratified analysis of cancer types showed that over expressed METTL3 was related to poor prognosis in digestive system cancer patients, including CRC(HR=2.29, 95%CI:1.50-3.49,P=0.0001) ,GC(HR=2.96,95%CI:2.13-4.12,P<0.00001),and liver cancer(HR=2.70,95%CI:1.88-3.88,P<0.00001). Meanwhile, the elevated METTL3 expression also affected the lymph node metastasis (OR=3.40,95%CI=1.58-7.33,p=0.002) ,vascular invasion (OR=2.04,95%CI=1.06-3.95,p=0.03) and the tumors progression (III/IV vs. I/II: OR = 3.72, 95% CI: 1.94 - 7.13, P < 0.0001).Conclusion: The existing analysis indicates that METTL3 is associated with low OS and DFS in cancer patients and may serve as a biomarker to assess prognostic value.