Plant leaf trichomes not only are an essential trait for taxonomy but also participate in the resistance to biotic and abiotic stress. Leaf trichomes vary significantly among different tea varieties, ranging from leaves with high trichome density to relatively glabrous leaves. Leaf trichomes are a crucial diagnostic characteristic in tea identification and taxonomy. In addition, trichomes are also a valued trait in tea production; leaf trichomes are generally considered to be associated with improved taste. However, the molecular mechanisms of trichome formation and the genetic control of trichome density in tea plants remain unknown. In this study, we identified a gene named TRANSPARENT TESTA GLABRA1 (CsTTG1), which encodes a WD-repeat protein and is associated with trichome formation in tea. The results also showed that CsTTG1 is highly expressed in the top bud of tea, which is consistent with trichome formation in this tissue. CsTTG1 encodes a protein localized in both the nucleus and cytoplasm. In addition, the transcription level of CsTTG1 was related to the length and/or density of the trichomes in different tea cultivars with diverse leaf trichome densities. Moreover, overexpressing CsTTG1 increased the number of trichomes in Arabidopsis thaliana. Collectively, our results indicated that CsTTG1 is involved in regulating trichome formation and that the expression level of CsTTG1 may be related to trichome density in tea plants. Our results may facilitate research on tea taxonomy and the adaptation of tea to its habitats.