Abstract: A vegetable sequence system(Cauliflower-Amaranth-Spinach) used by farmer was set up. Changes of soil mineral nitrogen in vegetable field were simulated by using nitrogen balance model. The loss of soil mineral nitrogen and Nitrogen Use Efficiency(NUE) were analyzed under traditional and improved water and N-fertilizer managements. The results showed that the average soil mineral nitrogen losses(the total of ammonia volatilization and denitrification and nitrate leaching) of vegetable field during Cauliflower and Amaranth and Spinach growth under improved conditions were about 9% and 8% and 18% of those of traditional water and nitrogen management. But NUE of Cauliflower and Amaranth and Spinach were 2.3 times and 3.2 times and 1.7 times as much as those of traditional water and N-fertilizer management. Yield of vegetable was not significantly different under improved and traditional water and N-fertilizer management practices.