We investigated the effects of nitrogen on root activity, key enzyme activities of nitrogen metabolism, and non-structural carbohydrates (NSC) in 3 tea varieties (Fuding dabai tea (FD),Baojing huangjin tea 1# (HJ1) and Baihaozao (BHZ)) with 4 ammonium nitrogen (N) treatments:without N deposition:N₀ (0 g), low N deposition:N₁ (11 g), medium N deposition:N₂ (22 g), and high N deposition:N₃ (33 g). The results showed that root activity increased significantly in N₂ and N₃ compared with the control, however, there were no differences between these two treatments. The GS and GOGAT activities in tea leaves increased after N treatment. Compared with the control, the total nitrogen content and soluble protein content in tea leaves generally increased following nitrogen treatment, significantly in the case of N₂ and N₃ in HJ1 (P<0.05). As the mass of N in the treatment increased, the NSC and total soluble sugars presented a tendency of increasing. However, the changes in starch content displayed varietal specificities in FD, HJ1 and BHZ. Changes in key enzymes involved in nitrogen metabolism and NSC content were observed after nitrogen treatment, which were different in the 3 tea varieties. Following N treatment, HJ1 showed higher GS and GOGAT activities, higher root activity, and a significant increase of nitrogen metabolites compares to FD and BHZ, which indicates a higher rate of nitrogen assimilation. The total NSC content and C/N changed less in HJ1, which had a better quality of higher free amino acid content, implying that HJ1 better maintain a carbon-nitrogen balance. Therefore, research on the activities of key enzymes involved in nitrogen metabolism and NSC in tea plants can provide a basis for evaluating the quality of tea varieties and improving the quality and nitrogen use efficiency of tea plants.