Tea aphids are a major insect pest of tea plants (Camellia sinensis
(L.) O. Kuntze), resulting in both tea production loss and tea quality decline. Secondary metabolites play vital roles in plant resistance against aphid feeding. Therefore, understanding changes in metabolites before and after tea aphid infestation is essential for the screening and breeding of aphid-resistant tea varieties. In the current study, metabolomics profiling, quantitative analysis of metabolites, and determination of phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) activities and proline (Pro) content were performed in new shoots of the ‘Echa 1’ tea variety infested with tea aphids, using non-infested plants as controls. Results showed that 35.4% of ‘Echa 1’ was colonized by tea aphids, suggesting that ‘Echa 1’ exhibited medium resistance to tea aphids. In parallel, significantly higher PPO activity, markedly higher soluble sugar, total flavonoid, and Pro contents, and significantly lower tea polyphenol content were found after aphid infestation. Eight significantly accumulated metabolites, including three primary metabolites and five secondary metabolites, were also detected. The three primary metabolites were all up-regulated in aphid-impacted shoots, which may confer precursors for secondary metabolite biosynthesis and modify the nutritional compounds utilized by tea aphids. The five secondary metabolites included jasmonate-isoleucine (JA-Ile) and four flavonoids. JA-Ile, responsible for defense-related signaling molecules, was significantly up-regulated after aphid-feeding, functioning in the activation of downstream defensive pathways, while the flavonoids served as defense compounds against the tea aphids. Taken together, these results suggest that JA-Ile, flavonoids, and Pro are important defensive compounds against tea aphids in tea plants.