Abstract: The issue of nitrogen loss in paddy soils was addressed， where nitrate nitrogen was prone to dissimilatory reduction to gaseous nitrogen. The research focused on the targeted screening of microorganisms in paddy soils that can dissimilate nitrate to ammonium， thereby retaining nitrogen. The selected strains were identified using morphological and 16S rDNA gene sequencing techniques. Further， the ammonium production capability of these strains was optimized through single factor experiments. The results indicated that strain S2， identified as Enterobacter asburiae， exhibited a strong ability to dissimilate nitrate to ammonium. Optimization experiments revealed that the optimal carbon source for the growth of Enterobacter asburiae S2 was sodium citrate， the optimal pH for growth was 7.0， the optimal carbon-to-nitrogen ratio was found to be 25， under which the maximum ammonium production increased to 34.84 mg/L.