RNA methylation is an important epigenetic modification. Recent studies on RNA methylation mainly focus on the m6A modification of mRNA, but very little is known about the m5C modification. NSUN2 is an RNA methyltransferase responsible for the m5C modification of multiple RNAs. In this study, we knocked down the NSUN2 gene in HepG2 cells by CRISPR/Cas9 technology and performed high-throughput RNA-BisSeq. An important tumor-related lncRNA H19 was identified to be targeted by NSUN2. Studies have shown that the expression of H19 lncRNA is abnormally elevated and has a carcinogenic effect in many types of tumors. Our results demonstrated that m5C modification of H19 lncRNA can increase its stability. Interestingly, m5C-modified H19 lncRNA can be specifically bound by G3BP1, a well-known oncoprotein which further leads to MYC accumulation. This may be a novel mechanism by which lncRNA H19 exerts its oncogenic effect. Besides, both the m5C methylation level and the expression level of H19 lncRNA in hepatocellular carcinoma tissues were significantly higher than those in adjacent non-cancer tissues, which were closely associated with poor differentiation of hepatocellular carcinoma (HCC). In conclusion, we found that H19 RNA is a specific target for the NSUN2 modifier. The m5C-modified H19 lncRNA may promote the occurrence and development of tumors by recruiting the G3BP1 oncoprotein. Our findings may provide a potential target and biomarker for the diagnosis and treatment of HCC.