Abstract: In this study, to provide a theoretical basis for the selection of slow-release nitrogen fertilizer application schemes in rice fields and for green and sustainable agricultural production, we sought to determine the optimal proportion of slow-release nitrogen fertilizer application and its effects on rice yield and greenhouse gas emissions. The effects of slow-release nitrogen fertilizer reducing substitution for conventional nitrogen fertilizer on rice yield and greenhouse gas (CO₂, N₂O, and CH₄) emissions during rice cropping season were quantitatively assessed in paddy fields under straw return in the middle and lower reaches of the Yangtze River Basin. The study included the following six treatments: no fertilizer control (CK), conventional fertilizer (CN), slow-release nitrogen fertilizer substitution for conventional nitrogen fertilizer based on the same nitrogen input (SRN), and 20%, 40%, and 60% nitrogen reductions (−20% SRN, −40% SRN, and −60% SRN) based on SRN. The results revealed that compared with the CK treatment, the highest rice yield (9.78 t∙hm⁻²) was obtained in plots receiving the SRN treatment, and that there were no significant differences between the −20% SRN and SRN treatments. Compared with CN treatment, the SRN and −20% SRN treatments were found to promote significant increases of 10.1% and 7.7% in the yields of rice, respectively (P<0.05), whereas the −60% SRN treatment contributed to a significant 11.2% reduction (P<0.05). Furthermore, compared with the CK treatment, all the other fertilization treatments were found to promote significant increases in the cumulative emissions of CO₂, N₂O and CH₄, as well as in the global warming potential of paddy field soils, with a similar trend of CN ≈ SRN > −20% SRN > −40% SRN > −60% SRN > CK. In addition, compared with CK treatment, the CN and SRN treatments contributed to significant increases of 10.3%−34.0% in greenhouse gas emission intensity (P<0.05), whereas compared with the CN treatment, treatments with slow-release nitrogen fertilizer substitution for conventional nitrogen fertilizer were found to be associated with significant reduction in greenhouse gas emission intensity ranging from 8.9% to 17.7% in paddy fields (P<0.05). Overall, our findings indicate that 20% reduction in slow-release nitrogen fertilizer substitution for conventional nitrogen fertilizer is the optimal proportion of slow-release nitrogen fertilizer reduction applied in paddy field in this area. Adopting such practices could contribute to substantially enhancing soil fertility and rice yield, reduce greenhouse gas emissions, and promote sustainable agricultural development.