Releasing large quantities of volatiles is a defense strategy used by plants to resist herbivore attack. Oenanthe javanica, a perennial herb of the Apiaceae family, has a distinctive aroma due to volatile terpenoid accumulation. At present, the complete genome and genetic characteristics of volatile terpenoids in O. javanica remain largely unclear. Here, the telomere-to-telomere genome of O. javanica, with a size of 1012.13 Mb and a contig N50 of 49.55 Mb, was established by combining multiple sequencing technologies. Comparative genome analysis revealed that O. javanica experienced a recent species-specific whole-genome duplication event during the evolutionary process. Numerous gene family expansions were significantly enriched in the terpenoid biosynthesis process, monoterpenoid, and diterpenoid biosynthesis pathways, which resulted in abundant volatile substance accumulation in O. javanica. The volatile terpenoids of O. javanica showed repellent effects on herbivores. Terpenoid biosynthesis was activated by wounding signals under exogenous stimuli. The TPS gene family was significantly expanded in O. javanica compared to those in other species, and the members (OjTPS1, OjTPS3, OjTPS4, OjTPS5, OjTPS7, OjTPS16, OjTPS18, OjTPS30 and OjTPS58) responsible for different terpenoid biosynthesis were functionally characterized. These results reveal the genome evolution and molecular characteristics of volatile terpenoids in the process of plant-herbivore interactions. This study also provides genomic resources for genetic and molecular biology research on O. javanica and other plants.