The effects of nitrogen and straw management on global warming potential (GWP) and greenhouse gas intensity (GHGI) in a winter wheat–summer maize double-cropping system on the North China Plain were investigated. We measured nitrous oxide (N₂O) emissions and studied net GWP (NGWP) and GHGI by calculating the net exchange of CO₂ equivalent (CO₂-eq) from greenhouse gas emissions, agricultural inputs and management practices, as well as changes in soil organic carbon (SOC), based on a long-term field experiment established in 2006. The field experiment includes six treatments with three fertilizer N levels (zero N (control), optimum and conventional N) and straw removal (i.e. N₀, N_opt and N_con) or return (i.e. SN₀, SN_opt and SN_con). Optimum N management (N_opt, SN_opt) saved roughly half of the fertilizer N compared to conventional agricultural practice (N_con, SN_con), with no significant effect on grain yields. Annual mean N₂O emissions reached 3.90 kg N₂O-N ha⁻¹ in N_con and SN_con, and N₂O emissions were reduced by 46.9% by optimizing N management of N_opt and SN_opt. Straw return increased annual mean N₂O emissions by 27.9%. Annual SOC sequestration was 0.40–1.44 Mg C ha⁻¹ yr⁻¹ in plots with N application and/or straw return. Compared to the conventional N treatments the optimum N treatments reduced NGWP by 51%, comprising 25% from decreasing N₂O emissions and 75% from reducing N fertilizer application rates. Straw return treatments reduced NGWP by 30% compared to no straw return because the GWP from increments of SOC offset the GWP from higher emissions of N₂O, N fertilizer and fuel after straw return. The GHGI trends from the different nitrogen and straw management practices were similar to the NGWP. In conclusion, optimum N and straw return significantly reduced NGWP and GHGI and concomitantly achieved relatively high grain yields in this important winter wheat–summer maize double-cropping system.