Abstract: Food security and global warming are major challenges for humanity. Promoting ratoon rice cultivation in single-season rice regions, where hydrothermal conditions are sufficient for one rice growing season but insufficient for two, can enhance yield, thereby safeguarding national food security. However, changes in greenhouse gas (GHG) emissions from paddy fields following the adoption of ratoon rice in these regions have not yet been reported. A year-long field observation was conducted in Taihu Lake Basin using static chamber and gas chromatography to monitor GHG emissions and grain yield to address this gap. Six cropping systems were examined: rice-wheat (RW), rice-oilseed rape (RO), rice-cabbage (RC), rice-Chinese milkvetch (RA), rice-fallow (RF), and rice-ratoon rice-Chinese milkvetch (Rr). The results showed that the annual CH₄ emissions of the single-season rice treatments (RW, RO, RC, RF, and RA) ranged from 43.8 to 134.8 kg(CH₄)·hm⁻², while that of the Rr treatment was 540.9 kg(CH₄)·hm⁻². Annual N₂O emissions ranged from 7.2 to 19.7 kg(N)·hm⁻² under the single-season rice treatments and was 4.3 kg(N)·hm⁻² under the Rr treatment. Correspondingly, annual grain yields ranged from 7.0 to 11.0 t·hm⁻² under the single-season rice treatments and reached 14.1 t·hm⁻² under the Rr treatment. Compared with the single-season rice treatments, the Rr treatment exhibited a 3.0 to 11.4 fold increase in annual CH₄ emissions, a 40.4% to 78.1% reduction in annual N₂O emissions, a 71.2% to 292.7% increase in total greenhouse gas emissions (TGHG), and a 34.4% to 101.6% increase in greenhouse gas emission intensity (GHGI). Specifically, the Rr treatment achieved a 43.0% increase in annual grain yield compared to that under the RW treatment. Compared with the single-season rice treatments, Rr treatment significantly reduced annual N₂O emissions. However, incorporating straw from the first-season rice crop into the soil led to a marked increase in CH₄ emissions during the ratoon season, resulting in a substantially higher TGHG in Rr treatment than in the five single-season rice treatments. In conclusion, ratoon rice cultivation in typical single-season rice regions can significantly enhance annual grain yield and increase GHGI. Therefore, it is recommended to strengthen water management in ratoon rice fields and delay straw incorporation until after the ratoon season harvest to mitigate CH₄ emissions, thereby achieving the dual objectives of high yield and emission reduction.