Abstract: The experiment was carried out in summer maize season in Beijing cinnamon soil to study subsoil denitrification and factors affecting denitrification. Acetylene inhibition method was used to measure denitrification in a static soil core incubation system. Soil cores from different soil depth up to 60 cm were collected together to be incubated in the jar near the experimental field for 24 hours. The results indicated that denitrification rate were great different between fertilizer N treatments in the surface soil layers. Reduced denitrification were also found in the subsoil, The nitrogen losses by denitrification in the 15～30cm soil layer was amounted to 10.7%～33.5% of that in the 0～15 cm, and the total nitrogen losses by denitrification in the 15～60cm soil layers were amounted to 14%～51% of that in the surface soil. Addition of carbon source greatly raised denitrification both in the 0～15 cm soil layer and 45～60cm soil layer. Discussion was made on factors affecting denitrification of subsoil in the cinnamon soil. Underestimation of N losses by denitrification in the field may be made without considering the subsoil denitrification.