Abstract: This study selected and processed three widely promoted tea varieties in Hunan Province—Zhuyeqi, Xiangfeicui, and Fuding Dabaicha—into seven congou black tea samples using traditional congou black tea processing techniques. The processing was conducted in three ways: single variety, a mixture of two varieties (1:1), and a blend of all three varieties (1:1:1). The aim was to explore how different combinations of fresh leaves from various tea varieties could enhance the quality of black tea during the summer and autumn seasons. The tea samples were comprehensively analyzed through sensory evaluation, physicochemical component detection, β-glucosidase (β-GC) activity testing, headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), odor activity value (OAV), and orthogonal partial least squares-discriminant analysis (OPLS-DA) to assess changes in tea quality components. The results indicated that the aroma and taste of the tea samples improved after mixing fresh leaves with increased levels of water-soluble substances, flavonoids, and polyphenols. Notably, when all three varieties were mixed, the tea exhibited a lasting floral honey aroma and an increased soluble sugar content, receiving the highest sensory evaluation scores. The peak of β-GC activity in the mixed fresh-leaf tea samples was delayed, which may be beneficial for releasing certain aroma compounds with pleasant floral and fruity scents. Thirteen essential differential aroma compounds were identified in the seven black tea samples, including hexanoic acid, benzaldehyde, linalool oxide, nonanal, etc., characterized by floral, fruity, floral and fruity, woody, and creamy attributes. In summary, the study found that mixing fresh leaves can enhance the aroma and taste of summer and autumn black tea to a certain extent, providing a theoretical basis for the practical application of utilizing coarse and mature fresh leaves and controlling the quality of black tea in future production.