Abstract: Sudangrass and ryegrass rotation is a new type of cropping system in Jianghan Plain, which has developed very fast in recent years. Effects of N application on yield and accumulation of N and C in forage grass and of total N and organic C in soil under a sudangrass/ryegrass rotation regime were studied for four years in a field experiment in Jianghan Plain. With increasing N application rate, total yield of forage grass increased in the seasons 2005-2006, 2006-2007, 2007-2008, and 2008-2009. Compared with N0 (no N application) treatment, the yield in N1 (total 337.5 kg N/ha in the rotation) treatment increased 243.5%, 234.0%, 153.6%, and 127.0% in the four successive seasons while yield in N2 (total 675 kg N/ha in the rotation) treatment increased by 313.1%, 339.9%, 231.7% and 222.8%. Increasing N application improved the accumulation of N and C for the rotation. Total accumulations of N and C in N1 and N2 treatments were 134.7%, 261.9% and 110.2%, 181.5% higher than that of the N0 treatment. With the growth of the sudangrass/ryegrass rotation, soil total N in the N1 and N2 treatments increased but this was slight in the N0 treatment. Soil organic C in N0, N1, and N2 treatments all increased, and were significantly correlated with the treatment. Compared with the original soil, soil C/N ratios in the N1 and N2 treatments changed only slightly while that in the N0 treatment increased significantly.