Abstract: Cucumber‘Zhongnong19’was used to investigate the effects of water and fertilizer coupling on several nitrogen metabolism enzymatic activities and related substance contents under soilless culture in greenhouse. Three single plant irrigation levels：87 L（W1），125 L（W2），162 L（W3），and three fertilization levels：64 L（F1），92 L（F2），119 L（F3）. The results showed that nitrate reductase（NR），glutamine synthetase（GS），glutamate synthase（GOGAT），glutamate dehydrogenase（GDH），nitrate nitrogen and soluble proteins content were remarkably influenced by different irrigation levels. Under the F1 level，several metabolism indexes of the W1 level were higher than other levels. Under the F2 level and F3 level，the W2 level was the best. Activities of NR，GS，GOGAT，GDH，nitrate nitrogen and soluble protein contents were remarkably affected by the fertilization levels，the order was F3 level，followed by F2 level and F1 level under the same irrigation levels. There was an obvious interaction between irrigation treatment and fertilization treatment. Correlation analysis showed that nitrogen metabolism enzymatic activities and related substance contents were positively correlated with yield，nitrate contents of fruit，free amino acid of fruit，soluble protein of fruit，soluble sugar of fruit.

Key words: cucumber, water and fertilizer coupling, greenhouse, soilless culture, nitrogen metabolism