Abstract: Changes of N metabolism in water spinach after applying different levels of quinhydrone in soil were studied by pot experiment.The results show that the activities of nitrate reductase,glutamate dehydrogenase and glutamine synthetase in water spinach leaves are enhanced,the contents of total N and protein are increased, but the content of free amno acid is decreased.The suitable level of quinhydrone for water spinach in pot experiment is 20～40mg/kg.