Abstract: The open field experiment was conducted in Dongbeiwang of Beijing suburb. Based on the nine-season vegetable experiment with long-term conventional and balanced nitrogen and water application(1999～2001), sweet corn as N-catch crop was planted in summer after cauliflower harvest in order to study the dynamic changes of nitrate leaching and effect on the next vegetable of spinach. During the experimental period, sweet corn grew fast showing strong absorbency for nitrogen. Nitrogen uptake could reach 205.6～246.1 kg/hm². Compared with that of fallow plot, soil NO^-₃-N content in the soil profile(0～60 cm) of sweet corn plot was effectively reduced, and decreased the leaching of nitrogen to deeper layer. Yield of sweet corn was still higher even without chemical nitrogen input. Net weight of spike reached 9.2～10.2 t/hm² FW, which achieved good economic benefit. Yield of spinach planted after sweet corn and after fallow showed no significant difference and reached 18.4～20.7 t/hm² FW. It was shown that the sweet corn is a suitable catch crop.