The effects of different urea levels on seasonal ammonia volatilization of summer maize were studied in the fluvo-aquic soils in the central part of North ChinaPlain，which provided a basis for rational application of nitrogen fertilizer andreduction of ammonia volatilization loss in farmland.Combining with the local farmers’ planting and nitrogen applicationhabits，eight levels of nitrogen application were setup，namely0(N0)，50(N1)，100(N2)，150(N3)，200(N4)，250(N5)，300(N6)and400(N7)kg·hm -2.Ammonia volatilization was determined by in situ determinationand continuous air extraction in closed chamber.The results showed that significant ammonia volatilization occurred insummer maize planting system after applying nitrogen fertilizer，and ammonia volatilization mainly occurred within 5 daysafter applying fertilizer.The peak ammonia volatilization rate appeared 1～ 3 days after applyingfertilizer.The maximumammonia volatilization flux of base fertilizer and topdressing reached N2.35，5.30 kg·hm -2·d-1，respectively，and the ammonia volatilization amount of base fertilizer were N 3.76～ 9.82 kg·hm-2 and N 5.79～ 27.29 kg·hm-2 ammoniavolatilization duringtopdressing.During the whole growth period of summermaize，ammonia volatilization increased with theincrease of nitrogen fertilizerapplication.Ammonia volatilization was relatively low under 200 kg·hm -2nitrogenapplication. The yield of summer maize was 10 721.87 kg·hm-2，which was higher than that of other nitrogen applicationtreatments.Itcan be seen that a reasonable amount of nitrogen fertilizer can take into account both yield and ecologicalenvironment.Under 200 kg·hm-2nitrogen fertilizer level in summer maize field in Beijingsuburb，the yield of summer maize is the highest andthe loss of ammonia volatilization is relativelylow.