Abstract: The experiment was carried out at Dalate County and two kinds of green manure crops （hairy vetch and common vetch）were cropped after wheat. The results were as the followings： The yield of hairy vetch （Vieia villosa Roth.） and common vetch （Vicia sativa L.） was 23.8 t/hm^2 and 20.1t/hm^2 respectively when they were ploughed down in the first autumn. In the following year, when the N fertilizer was decreased by 30% the yield of wheat decreased by 4.4% and 5.8% if the hairy vetch and common vetch were cropped in the last year and decreased by 10.1% if without any green manure. When the N fertilizer was decreased by 60% the yield of wheat decreased by 15.6% and 13.7% if the hairy vetch and common vetch were Cropped in the last year and decreased by 17.6% if without any green manure. So the green manure cropping could increase the N supplying of the soil.