Centella asiatica is a medicinal plant containing various ursane-type saponins that serve as a model system for studying triterpenoid accumulation. We assembled a haplotype-resolved genome for C. asiatica, and it showed allelic imbalance between haplotypes. The genome underwent one whole-genome duplication event followed by chromosomal fusion resulting in the current karyotype. We also constructed the metabolic regulatory network of triterpenoid saponins and found that triterpenoid biosynthesis was accompanied by gene duplication. These findings may assist in mining genes for the metabolism of C. asiatica and improving the understanding of the genetic basis for the diversity of triterpenoid biosynthesis.