Using“Omega”purple cabbage as the test material，field experiment was conducted to study the difference in nitrogen metabolism related enzyme activity and yield of purple cabbage leaves under different water and fertilizer coupling conditions.The local traditional water and fertilizer management(N 466.5 kg/hm²，P2O5 756 kg/hm²，K2O 269.91 kg/hm²，flood irrigation and spraying) was designed as control(CK).The treatment was designed with two factors.The first factor was the lower limit of irrigation，which included three gradients: W1(80% of the maximum field water capacity)，W2(60% of the maximum field water capacity)，W3(40% of the maximum field water capacity).The second factor was fertilization，which included three fertilization gradients:F1(local traditional fertilization)，F2(80% local traditional fertilization)，F3(60% local traditional fertilization).Compared with CK，the chlorophyll content，nitrogen metabolism related enzyme activity，soluble protein content，dry matter accumulation and yield of purple cabbage increased significantly and reached the highest values W2F2.Under the same amount of irrigation，the activities of NR，GDH，GOGAT and GS，as well as the contents of soluble protein，dry matter，chlorophyll and yield all increased first and then decreased with the decrease of fertilizer application.Under the same amount of fertilizer application，the activities of NR，GDH，GOGAT，GS，soluble protein content，chlorophyll content and yield all reached the peak value when the irrigation lower limit was 60%.W2F2(field capacity 60%，373.2 kg/hm²，604.8 kg/hm²，215.93 kg/hm² for N，P，K) is the best treatment，which can improve the activity of nitrogen metabolizing related enzymes in functional leaves of purple cabbage.Compared with the local traditional water and fertilizer treatment，it can increase production by 16.37%，save water by 58.27%，and save fertilizer by 20%.