【Objective】This study aimed to reveal the effects of biogas slurry instead of chemical nitrogen fertilizer on soil Denitrification (Den) and Dissimilatory nitrate reduction to ammonium (DNRA).【Method】A field plot experiment was carried out in a typical coastal paddy field in Dongtai, Jiangsu Province. Five treatments were set up: a single application of chemical fertilizer (C), a single application of biogas slurry (B), combined application of biogas slurry and straw (BS), combined application of chemical fertilizer and straw (CS) and control (CK). The variation characteristics of soil Den and DNRA potential at different growth stages of rice plants were studied by the ¹⁵N isotope tracer technique.【Result】The results showed that: (1) In the whole rice growth period, Biogas slurry instead of chemical fertilizer effectively reduced the Den intensity (1.48 μg·kg^-1·h^-1) and the total amount of N₂O by 27% in paddy soil. Compared with the combined application of chemical fertilizer and straw, the combined application of biogas slurry and straw resulted in a significant increase in total N₂O (70%).(2) Looking at different growth stages, the regulation of N₂O in the mature stage of the plant is particularly necessary. The N₂O production in biogas slurry (B, BS) and chemical fertilizer (C and CS) treatments peaked at maturity, accounting for 70%～71% and 75%～92% of the total production on average, respectively. Also, the soil DNRA potential was the highest at tillering stage, and the DNRA potential of B and BS treatments were significantly higher than that of C and CS treatments. (3) The Den potential of biogas slurry or chemical fertilizer treatment was positively correlated with pH and negatively correlated with C: N. Also, the increase in C: N resulted in a decrease in Den intensity of biogas slurry instead of chemical fertilizer (i.e. treatment B). When combined with straw, the factors leading to changes in Den potential are transformed into NO₃^--N and NH₄⁺-N, and the decrease of C: N leads to an increase in Den intensity.【Conclusion】Biogas slurry instead of chemical fertilizer can play a positive role in the preservation of nitrogen in soils. This study provides a theoretical basis for clarifying the impact of biogas slurry replacing chemical fertilizer and straw returning on the process of Den and DNRA in paddy soils. Also, it highlights the environmental impact as well as the exploration of biogas slurry application mode in coastal farmland.