Abstract: 【Objective】 In order to identify the genes that regulate the growth and development of the Hirudo nipponia, and to reveal the molecular mechanisms of growth and development, reproduction and anticoagulation, so as to provide a theoretical basis for the breeding, growth and development, and studies on related functional genes of H. nipponia.【Method】 H. nipponia were studied at the larval stage(within 10 d of hatching, HNL), young stage(about 2 months after hatching, HNY) and adult stage(about 2 years after hatching, HNA). Using the Illumina HiSeq 4000 platform to transcriptome sequencing of cDNA library. Differentially expressed genes(DEGs) were screened by false discovery rate (FDR) <0.05 and|log₂ FC|>1, and then to perform GO functional annotation and KEGG signal pathway enrichment analysis.【Result】A total of 541124257 raw reads were generated from 24 cDNA libraries using samples from three stages. There were 20430 mRNAs transcripts were obtained by Fastp quality control and RNA-Seq assembly and 88 new mRNAs transcripts were annotated. A total of 1348 DEGs were obtained by two-by-two comparison of different growth stages of the H. nipponia, including 238 DEGs in HNL vs HNY, 976 DEGs in HNL vs HNA, and 763 DEGs in HNY vs HNA. DEGs of HNL vs HNA were mainly enriched in GO functional items such as proteolysis, myosin complex, cytoskeleton, chitin metabolism and response to injury, phenylalanine/tyrosine/tryptophan biosynthesis, acrylamide transferase and other KEGG signal pathways. These changes revealed that larvae fed a lot during growth to provide energy for their own development through digestion, metabolism and synthetic of substances. After adult H. nipponia grew and matured, metabolic processes related to their growth and development were down-regulated. Moreover, adult H. nipponia have adapted to the environment, and their sensitivity to environmental stimuli was also reduced.【Conclusion】 Among the 976 DEGs obtained from HNL vs HNA, the up-regulated DEGs are mainly related to muscle development, whereas the DEGs related to gonadal development, ovarian regulation and neurodevelopment are obviously periodic, and the expression changes of all these genes are related to the growth and development of H. nipponia. Hirudin and anticoagulation-related genes are highly expressed in young stages, so it is suitable to use young H. nipponia when performing studies on the anticoagulant ability of leeches.