A field experiment was conducted to study effect of timing of application of dicyandiamide (DCD) on N₂O emission from the wheat cropping system. Four treatments, including CK (the control with urea alone), DCD-B (application of DCD together with basal fertilizer), DCD-T (application of DCD with the top dressing fertilizer) and DCD-BT (application of DCD with basal fertilizer and the top dressing, respectively), were designed and implemented separately during the wheat growing period. Results indicate that compared with CK, application of DCD inhibited N₂O emission, which was reduced by 21%、26% and 35%, respectively, from Treatments DCD-B、DCD-T and DCD-BT (P <0.05). It was observed mainly during the sowing-greening stage in Treatment DCD-B, during the greening-maturing stage in Treatment DCD-T, and during the whole wheat-growing stage in Treatment DCD-BT. From seasonal variation of N₂O flux during the wheat-growing period, compared with CK, the first max-fluxes N₂O emission (16d after applying basal fertilizers) were significantly decreased from Treatments DCD-B and DCD-BT; the second was significantly reduce from Treatments DCD-T (P <0.05). Soil NH⁺₄-N contents and apparent nitrification rate of NH⁺₄-N in soil were higher in treatments treated with DCD than in the treatment without DCD. Moreover, the soil NH⁺₄-N contents decreased with the time elapsing. During the sowing-greening stage, soil NH⁺₄-N contents and apparent nitrification rate of NH⁺₄-N in soil were higher in Treatments DCD-B and DCD-BT than in Treatments DCD-T and CK; and during the greening-maturing stage, in Treatments DCD-T and DCD-BT than in Treatments DCD-B and CK. Compared with CK, Treatments DCD-B and DCD-BT increased significantly in grain yield (P <0.05), while Treatment DCD-T did not differ much (P >0.05). Based on these findings, the application of DCD with basal fertilizer and the top dressing respectively (Treatment DCD-BT) has the highest N₂O emission inhibiting efficiency and is the best management practice for DCD application for mitigating greenhouse gas emission from the wheat system, as the method reduces N₂O emission from the wheat system while increasing wheat yield; the effect of Treatment DCD-B or Treatment DCD-T on N₂O emission in the wheat system is influenced not only by timing of DCD application, but also by interannual variation of precipitation and irrigation. The results suggest that in the cropping systems with irrigation, the best application method of DCD is the application of DCD with basal fertilizer and the top dressing respectively (Treatment DCD-BT); in the cropping systems with no irrigation, if there is no condition to apply DCD with basal fertilizer and the top dressing respectively, application of DCD with basal fertilizer should be adopted in the area where the precipitation is heavier in winter than in spring, while application of DCD with the topdressing fertilizer should be adopted in the area where the precipitation is heavier in spring than in winter. Accroding to interannual variation of precipitation and irrigation, different timing of DCD application has the highest inhibiting efficiency of inhibitors on N₂O emission during the wheat growing system.