Using soil probe techniques, we in situ measured changes of N2O concentration at different soil depths of loess soil profile in a long term field experiment were measured from 1999 to 2001. The experimental results proved denitrification in deep layer of loess soil. Meanwhile, N2O concentration in soil profiles had remarkable temporal and spatial variation. The annual N2O concentration variation changed with the climate condition and management practice. There was higher N2O concentration in soil profiles in the year when the annual precipitation was higher than normal. N2O peaks often appeared after the irrigation or rainfall. The average N2O concentration during corn growing season was greater than that during winter wheat season, mainly due to the higher temperature and rainfall amount in the summer season. The N2O concentration in the soil profiles were in the order of 60cm ≈ 90cm ≈150cm＞ 30cm＞ 10cm for control treatment, and those in the order of 60cm > 90cm ≈150cm＞ 30cm＞ 10cm for N fertilized treatment. The subsoil denitrification was the main N2O source of subsoil in loess soil. Appling nitrogen fertilizer would definitely increase N2O concentration in soil profiles.