The initiation and progression of diffuse large B-cell lymphoma (DLBCL) is governed by genetic and epigenetic aberrations. As the most abundant eukaryotic message RNA modification, N6-methyladenosine (m6A) is known to influence various fundamental bioprocesses by regulating target gene; however, the function of m6A modifications in DLBCL is unclear. PIWI-interacting RNAs (piRNAs) have been indicated to be epigenetic effectors in cancer. Here, we show that high expression of piRNA-30473 supports the aggressive phenotype of DLBCL, and piRNA-30473 depletion decreases proliferation and induces cell cycle arrest in DLBCL cells. In xenograft DLBCL models, piRNA-30473 inhibition reduces tumor growth. Moreover, piRNA-30473 is significantly associated with overall survival (OS) in a univariate analysis, and is statistically significant after adjusting for the National Comprehensive Cancer Network-International Prognostic Index (NCCN-IPI) in the multivariate analysis. Additional studies demonstrate that piRNA-30473 exerts its oncogenic role through a mechanism involving the upregulation of WTAP, an m6A mRNA methylase, thus enhances the global m6A level. Integrating transcriptome and m6A-seq analyses reveal that WTAP increases the expression of its critical target gene HK2 by enhancing the HK2 m6A level, thereby promoting the progression of DLBCL. Together, the piRNA-30473/WTAP/HK2 axis contributes to tumorigenesis by regulating m6A RNA methylation in DLBCL. Furthermore, by comprehensively analyzing our clinical data and datasets, we discover that the m6A regulatory genes piRNA-30473 and WTAP improve survival prediction in DLBCL patients. Our study highlights the functional importance of the m6A modification in DLBCL and might assist in the development of a prognostic stratification and therapeutic approach for DLBCL.