In this study, the gene encoding bHLH transcription factor, named CsbHLH137 (GenBank accession OL332046), was cloned from Camellia sinensis cv. ‘Mengshan 9’ by PCR based on the genome data of tea plant. Sequence analysis showed that the open reading frame length of CsbHLH137 was 1 023 bp, encoding 340 amino acids. Analysis of protein sequence characteristics showed that the CsbHLH137 protein contained HLH binding domain with a molecular weight of approximately 38.59 kD and the theoretical isoelectric point of 5.59. The bHLH protein involved in response and interaction to light through the constituent domains of the circadian clock. CsbHLH137 transcription factor was a hydrophilic protein, including four unordered regions and 20 phosphorylation sites, and mainly composed of αhelix and random coil. The analysis of stomatal aperture and photosynthetic parameters of tea leaves at different time points showed that compared with the dark treatment, the regulation of stomatal aperture was remarkable for the light treatment, and the photosynthetic parameters G_s, C_i, and T_r fluctuated greatly during the day and maintained a relatively stable state at night. The expression profiles of CsbHLH137 in ‘Mengshan 9’ under the regulation of the circadian clock were detected by RTqPCR. The results showed high and peak expression of the CsbHLH137 gene during the day and maintenance of low expression level at night. It was predicted that the CsbHLH137 was the DELLAresponsive gene and played a role on photomorphogenesis.