Soil carbon sequestration is widely considered to improve soil quality, safeguard food security, and mitigate climate change. However, the effect of best management practices like conservation tillage on soil carbon sequestration remains unclear. A 3-year field experiment was conducted to explore the effect of integrated straw-tillage systems (conventional rotary tillage, CT; no-tillage, NT; CT with straw retention, CT-SR; NT with straw retention, NT-SR) on maize productivity, soil organic carbon (SOC), and net ecosystem carbon budget (NECB) in Southwest China. The results indicate that the CT-SR achieved the highest grain yield (9.1 Mg ha^-1) and aboveground biomass (19.0 Mg ha^-1). Averaged grain yield and aboveground biomass of the two systems without straw retention, CT and NT, were, respectively, 4.5 % and 4.1 % lower than those with straw retention. The NT-SR and CT-SR achieved the highest SOC concentration, 12.3 g kg^-1 and 11.9 g kg^-1, respectively, as well as the highest SOC stock and the annual increase in SOC and SOC stock. The highest NECB was observed in NT-SR, which was not significantly different from those of CT-SR and CT, but was higher than that of NT by 13.1 %. Higher SOC sequestration was the major contributor to the NECB of NT-SR, while higher gross primary productivity and harvest carbon removal contributed mostly to NECB of CT-SR and CT. A combination of straw retention and NT was more positive than that with CT for the continued rise in SOC sequestration. The NT system was inferior to others for improving the system productivity and NECB, especially when comparing with CT-SR. In summary, the integrated straw retention and rotary tillage (CT-SR) achieved the highest system productivity, while the NT-SR was superior for SOC sequestration and NECB than other systems for maize production in the Southwest China. An integrated straw-tillage management is therefore an efficient and feasible way to maintain high maize productivity and carbon sustainability.