[Objective] This study aims to investigate the effect of Al₂(SO₄)₃ combined with organic materials on the nitrogen conversion mechanism in saline-alkali soil，and to reveal the effects of different application ratios on soil nitrogen pool. [Methods] This study was conducted on soda saline-alkali soils in the western part of Jilin Province. Three Al₂(SO₄)₃ gradients were applied，corresponding to 0.2%A_0.2，0.1%A_0.1 and 0%A₀ of soil weight，along with three straw gradients，corresponding to 1%S₁，0.6%S₀.6 and 0%S₀ of soil weight. The contents of soil NH₄⁺-N and NO₃^--N，as well as the activities of urease and protease，were measured under both nitrogen fertilization and no nitrogen fertilization conditions. [Results] The application of Al₂(SO₄)₃ improved the average net mineralization and nitrification rates，with the performance of A_0.2S₀>A_0.1S₀. These rates gradually decreased over the incubation period. Incorporating straw into the soil suppressed nitrogen mineralization and nitrification. Despite this suppression，the application of urea fertilizer significantly increased the average net mineralization rate by 17.34 times and the nitrification rate by 3.61 times. However，the inhibitory effect still remained. The combined application of Al₂(SO₄)₃ and rice straw（A_0.1-0.2S_0.6-1）further suppressed the conversion of soil nitrogen. In treatments with high levels of rice straw（S>_0.6），the addition of Al₂(SO₄)₃ accelerated the decline in soil NH₄⁺-N and NO₃^--N levels，which was alleviated by the application of nitrogen fertilizer. Furthermore，the changes in ammonium and nitrate nitrogen contents increased with higher Al₂(SO₄)₃ application rates，following the order of A_0.2S₁>A_0.2S_0.6>A_0.1S₁. The interaction between Al₂(SO₄)₃ and rice straw had significant effects on urease and protease activity，soil total nitrogen，and the concentrations of NH₄⁺-N and NO₃^--N in the absence of urea application. These effects became highly significant following urea application Additionally，significant positive correlations were observed between urease and protease activity and total nitrogen content，between NH₄⁺-N and NO₃^--N，and between net mineralization rate and nitrification rate in the soil. [Conclusion] The combined application of Al₂(SO₄)₃ with high rice straw retains more nitrogen in the soil，with the A_0.2S₁ treatment demonstrating the most efficient nitrogen utilization. These findings offer valuable insights for the reclamation and management of saline-alkali soils and provide a theoretical foundation and practical guidance for future research and application in this field.