Abstract: Taking ‘Italian Resistant-bolting tolerance（208）（Lactuca sativa L.）’ lettuce as test material, hydroponics was used as treatment, three nitrogen application levels N4(4 mmol·L^-1),N8(8 mmol·L^-1),N12(12 mmol·L^-1) and four intermittent nitrogen application frequencies F0（0 day）,F3（3 days）,F6（6 days）,F9（9 days） were set, the effect of different nitrogen application levels and intermittent nitrogen application frequency on the growth status, flavonoids, total phenols, anthocyanins and ascorbic acid contents, nitrate and nitrite contents of lettuce during harvesting period were studied, in order to provide reference for improving the nutritional quality of lettuce in hydroponics.The results showed that continuous nitrogen application（F0） could improve the plant height and aboveground fresh weight of lettuce.Under the N8 level, aboveground fresh weight of lettuce became lower and lower with the increase of nitrogen application interruption frequency.8 mmol·L^-1,when the frequency of intermittent nitrogen application was 6 days, the content of ascorbic acid and nitrite reductase was the highest, which was 83.68% higher than that of the lowest N12 F9,and the content of nitrite reductase was 60.79% higher than that of the lowest N12 F3.Nitrate content was the lowest.Therefore, the nitrogen application level of 8 mmol·L^-1 and the intermittent nitrogen application frequency of 6 days could ensure the growth of plants, increase the content of ascorbic acid, and reduce the accumulation of nitrate at the same time.