A closed continuous airflow method was used to study on dynamic changes of NH3 volatilization in treatments with ammonium bicarbonate(NC) and urea(UR) in typical doublecropping paddy field in Hunan Province.The results showed that,1) both of the initial NH3 volatilization intensity and total NH3 volatilization quantity from NC treatment were higher than those of the UR treatment.2) in early rice field,NH3 volatilization quantity of the NC treatment was 45.19 kg·hm2,accounting for 30.12% of N application amount; and that of the UR treatment was 32.93 kg·hm2,accounting for 21.95% of N application amount; but in late rice field,NH3 volatilization emissions of the NC treatment was 70.91 kg·hm2,the loss rate was 31.93%; and that of the UR treatment was 61.78 kg·hm2,and the loss rate was 27.04%. 3) urea as basal dressing could significantly reduce emissions of NH3 volatilization,and decreased the N losses.