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Abstract Background Caffeic acid O-methyltransferase (COMT) is a key enzyme that regulates melatonin synthesis and is involved in regulating the growth, development, and response to abiotic stress in plants. Tea plant is a popular beverage consumed worldwide, has been used for centuries for its medicinal properties, including its ability to reduce inflammation, improve digestion, and boost immune function. By analyzing genetic variation within the COMT family, while helping tea plants resist adversity, it is also possible to gain a deeper understanding of how different tea varieties produce and metabolize catechins, then be used to develop new tea cultivars with desired flavor profiles and health benefits. Results In this study, a total of 25 CsCOMT genes were identified based on the high-quality tea (Camellia sinensis) plant genome database. Phylogenetic tree analysis of CsCOMTs with COMTs from other species showed that COMTs divided into four subfamilies (Class I, II, III, IV), and CsCOMTs was distributed in Class I, Class II, Class III. CsCOMTs not only undergoes large-scale gene recombination in pairs internally in tea plant, but also shares 2 and 7 collinear genes with Arabidopsis thaliana and poplar (Populus trichocarpa), respectively. The promoter region of CsCOMTs was found to be rich in cis-acting elements associated with plant growth and stress response. By analyzing the previously transcriptome data, it was found that some members of CsCOMT family exhibited significant tissue-specific expression and differential expression under different stress treatments. Subsequently, we selected six CsCOMTs to further validated their expression levels in different tissues organ using qRT-PCR. In addition, we silenced the CsCOMT19 through virus-induced gene silencing (VIGS) method and found that CsCOMT19 positively regulates the synthesis of melatonin in tea plant. Conclusion These results will contribute to the understanding the functions of CsCOMT gene family and provide valuable information for further research on the role of CsCOMT genes in regulating tea plant growth, development, and response to abiotic stress.