To explore the effects of different tillage methods and straw returning treatments on soil organic carbon and annual yield of rice and wheat，long-term positioning experiments were conducted on the experimental farm of Yangzhou University from the autumn sowing of 2001. A total of six treatments were set up in the experiments，including no-tillage and straw returning of rice and wheat continuously(NTS)，convention tillage for wheat and no-tillage for rice(RT1)，convention tillage for rice and no-tillage for wheat(RT2)，convention tillage and straw returning in rice and wheat continuously(CTS)，minimum tillage and straw reduced returning in rice and wheat continuously(MTS)，convention tillage and no straw returning in rice and wheat continuously(CT). The soil organic carbon content was measured after rice harvest. The results showed that:(1)Straw returning significantly increased soil organic carbon content. Compared with the CT treatment，the soil organic carbon content of the NTS，RT1，RT2，CTS and MTS treatments were increased by 13.29%，4.76%，8.18%，19.88% and 21.34%，respectively，in average within 20 years.( 2)The NTS treatment showed a greater impact on the soil surface organic carbon content，with an increase by 14.49%-39.02% as compared with other tillage methods. In the RT1，RT2，CTS and MTS treatments，topsoil organic carbon content in a balanced way was increased.( 3)The yield of rice and wheat was higher in the CTS and MTS treatments，with 3.68% and 4.09% increase compared with CT treatment，respectively. The yield of rice and wheat was decreased by 3.48% in NTS treatment compared with CT treatment. The result indicates that the combination of moderate straw return and minimum tillage has the most significant effect on improving soil organic carbon and yield，which is the most suitable tillage method for the studied area.