It is important to investigate straw decomposition，nutrient release and soil organic carbon under different maize straw returning methods and nitrogen fertilizer managements in wheat-maize rotation area of North China Plain. Based on a 2-year field experiment，this study investigated dynamic changes of straw decomposition and soil organic carbon using nylon net bag method under two straw returning methods (RT:straw rotary tillage and DT:deep tillage) and three nitrogen application levels (N1:180 kg/hm²，N2:240 kg/hm² and N3:300 kg/hm²). The results showed that straw decomposition rate of each treatment showed a trend of fast change in the early stage，then slow change and finally tended to stagnate. The straw returning method and nitrogen application level significantly affected straw decomposition characteristics. The straw decomposition rate with DT treatments was significantly higher than those of RT treatments，increased by 4.36%-6.25%. The straw decomposition rate increased with the increase of nitrogen fertilizer application level in the early straw decomposition stage，but there was no significant difference among the nitrogen fertilization treatments in the late stages. The two factors of straw returning method and nitrogen application rate had interaction on the cumulative release of straw carbon. The rate of straw carbon release was higher with N1 than other nitrogen levels under RT treatment，but was higher with N3 than other nitrogen levels under DT treatment. The straw returning method and nitrogen application rate significantly affected the soil organic carbon content，and had an interactive effect. The soil organic carbon content with RT treatment was significantly higher than that of DT treatment during wheat growth period in 0-20 cm soil layer，and soil organic carbon content was increasing with nitrogen application level，but there was an opposite trend in 20-40 cm soil layer. The straw returning method and nitrogen application level had a significant influence on wheat yield and its components，and had an interactive effect on wheat yield. The wheat yield under DT treatment was higher than RT treatment，and increased by 4.26% and 3.41% in two years. Under RT treatment，wheat yield with N1 was higher than other nitrogen levels，but under DT treatment，N2 and N3 were more conducive to increasing wheat yield. Under the conditions of this study，integrated straw deep ploughing returning and nitrogen fertilizer of 240 kg/hm² could promote straw decomposition and its carbon release，increase organic carbon in surface and sub-surface soil and wheat yield，while straw rotary tillage returning with nitrogen fertilizer of 180 kg/hm² was more conducive to increasing soil organic carbon in surface soil and wheat yield.