[Aim]  To identify the Ostrinia furnacalis juvenile hormone acid O-methyltransferase (OfJHAMT) gene, and to investigate its role in diapause in this species. [Methods]  Based on O. furnacalis transcriptome data previously obtained by our lab (NCBI accession number : PRJNA1030200 ), the OfJHAMT gene was cloned and identified with RT-PCR and analyzed using bioinformatics. The expression of the OfJHAMT gene in different diapause stages of O. furnacalis larvae was analyzed using real-time fluorescent quantitative PCR (qPCR), and its function during the diapause process was investigated using RNA interference (RNAi; injecting dsRNA into diapausing larvae). [Results]  The open reading frame (ORF) of the OfJHAMT gene is 948 bp long, encodes 315 amino acids, and has a predicted protein molecular weight of 36.40 kD and an isoelectric point (pI) of7.64. Homologous sequence alignment and phylogenetic analysis indicate that OfJHAMT is most closely related to the OnJHAMT gene of the European corn borer, Ostrinia nubilalis, with which it has an amino acid sequence identity of 96.51%. The OfJHAMT gene was expressed in all diapause stages, with the lowest relative expression during the diapause period. Expression levels increased after diapause ended. The RNAi experiment indicated that expression of OfJHAMT was downregulated by 86.35% 48 h after the injection of dsRNA. The survival rate of larvae dropped to 56.67% by the 9th day after injection, and, compared to the dsGFP control group, the diapause rate of the treatment group was 81.67% lower. In addition, larvae treated with dsRNA exhibited different degrees of cuticle darkening, tissue softening, and wrinkling, phenotypes that were often lethal, with surviving individuals mostly being deformed pupae that were unable to develop normally into adults. [Conclusion]  The OfJHAMT gene appears to play an important role in the diapause process of O. furnacalis larvae.