【Objective】The expansion of bamboo forests leads to environmental heterogeneity within the tea plantation ecosystem, exerting a significant impact on the growth of tea plants and the quality of tea leaves. Unveiling the potential effects of bamboo forest expansion on the growth of tea plants and the quality of tea leaves is paramount for the scientific management of tea plantations undergoing bamboo expansion.【Method】The study focused on the continuous patches of bitter bamboo (Pleioblastus amarus) and tea (Camellia sinensis) tree expansion forests in Longyou County, Zhejiang Province. Three types of plots were established, namely, the tea-bamboo mixed forest interface zone, the mixed forest center zone, and the pure tea plantation zone. Various parameters, including growth characteristics, tea pigments, tea polyphenols, caffeine, free amino acids, and mineral nutrients in tea leaves, were measured. The differences in the growth characteristics of tea trees and tea leaf quality after the expansion of P. amarus into tea plantation were analyzed using multivariate statistical methods, orthogonal partial least squares-discriminant analysis, and variable projection importance methods.【Result】(1) The expansion of P. amarus significantly influences the growth and branching number of tea plants, with a notable impact on the average height (P< 0.05). (2) With the expansion of P. amarus into tea plantations, there was no significant impact on the pigment content of tea leaves. However, there was a significant effect on the chlorophyll a/b of tea leaves in the mixed forest interface zone (P<0.05). The impact of pigments did not significantly contribute to tea leaf quality. (3) Influenced by the expansion of P. amarus, the contents of tea polyphenols and caffeine in the interface zone were significantly lower than those in the mixed forest center and pure tea plantation zones (P<0.05). The change in ratio of phenol to ammonia was not obvious, and all three parameters contribute significantly to tea leaf quality. (4) With the expansion of P. amarus into tea plantations, there was an increasing trend in the content of the 14 free amino acid components in tea leaves. However, in the mixed forest interface and center zones, the contents of methionine and cysteine were significantly higher than in the pure tea plantation zone (P<0.05). The content of serine was highest in the mixed forest center zone, but the change was not obvious. All three amino acids contributed significantly to tea leaf quality. (5) With the expansion of P. amarus into tea plantations, there was a significant decrease (P<0.05) in the content of calcium, manganese, magnesium, iron, and copper elements in tea leaves. These elements were noticeably accumulated in the mixed forest interface zone, while the zinc content exhibited an opposite trend. The variations in these mineral nutritional elements contribute significantly to the differences in tea leaf quality.【Conclusion】The expansion of P. amarus induced changes in the growth strategy of tea trees, altered the composition of effective components and mineral nutrient elements in tea leaves, thereby influencing tea quality and hindering its improvement.