Caligula japonica is a forestry pest due to its damage to multiple trees. Recently, it served as a potential natural medical mesh biomaterial in the medical industry. However, studies on karyotype evolution and functional genomics of C. japonica are limited by the absent of genomic resource and its several months of diapause. Here, we conducted high-throughput sequencing of its genome and firstly obtained the chromosome-level genome. we successfully assembled a high-quality genome of 584,506,556bp with Contig N50 of 12 Mb and 31 chromosomes. About 342 Mb repeat sequences were identified, accounting for 58.53% of C. japonica genome. Genome annotation by de novo gene prediction and homologous gene search yields 24791 protein-coding genes. We also applied manual annotation of diapause genes in C. japonica genome. The genome abstained in this research will not only support resource for future study on diapause mechanism of C. japonica but also help to progress comparative genomic analyses in Lepidoptera.