Accumulation and movement of NO₃^--N in soil profile in winter wheat/summer maize rotation system was studied in field experiments.The results showed that nitrification completed in 7d after urea was applied into soil.High concentration of NH₄⁺-N only appeared in short period after fert ilization and NH₄⁺-N concentration in other t imes was 1~3 mg kg^-1.NH₄⁺-N concentration in different soil layers was lower than 4 mg kg^-1 generally.So the content of NH₄⁺-N could not reflect soil available nitrogen level.NO₃^--N in soil profile was significantly increased with nitrogen fertilizer rate increasing.NO₃^--N movement mainly occurred in 0~40 cm with low nitrogen rate(N<120 kg hm^-2),but large amount of NO₃^--N moved below 100 cm even in winter wheat growth season with high nitrogen rate.The movement of NO₃^--N had a great different between years.In drought year,the possibility of NO₃^--N moving to deeper layer was low even in summer maize growth season.Except large amount of gas loss occurred in 1999 summer maize season(extremely drought in this season),the loss nitrogen fertilizer mainly accumulated in deeper layer in other season,which was consistent in two sites.