Ecological restoration of abandoned farmland is a widely adopted strategy to enhance the function and sustainability of degraded ecosystems, which has profound implications for soil nitrogen (N) cycling, especially denitrification N gas loss. However, the response of denitrification and potential nitrous oxide (N2O) emissions via denitrification to ecological restoration following farmland abandonment in the rainy season remains unclear, particularly in fragile ecosystems. Here, we conducted a 21-day incubation experiment using the acetylene inhibition method to assess denitrification rates and N2O emissions during the denitrification process, while exploring how changes in soil edaphic and microbial properties affect gaseous N emissions under natural vegetation restoration of abandoned farmland (cultivated land, degraded sloping farmland, shrubland, and forest land) in the dry-hot valley of southwest China. The results indicated that land degradation (degraded sloping farmland) had a stronger effect in reducing denitrification than cultivated land, and denitrification gradually increased along the restoration trajectory toward forest land. Notably, under denitrification conditions, although vegetation restoration was beneficial for N2O mitigation, the abundance of denitrifying genes (nirS and nirK) increased by 130 % after natural restoration, showing an inconsistent trend with denitrification rates. Variance partitioning analysis indicated that the individual effects of soil N substrate (40.2 %) and its interactions with soil microbial and physicochemical properties (26.7 %) explained most of the variations in denitrification during the restoration, with soil nitrate content being the key factor. Overall, our findings highlight the significance of soil substrate availability in regulating gaseous N loss following natural restoration, which is helpful for better predicting the process of N loss regulated by ecological restoration in semi-arid degraded ecosystems.