[Objective]In order to study 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]Three Al2(SO4)3 gradients accounting for 0.2%A0.2，0.1%A0.1 and 0%A0 of soil weight and three straw gradients acco unting for 1%S1，0.6%S0.6 and 0%S0 of soil weight were set up in the west of Jilin Province. Soil NH4+-N content, NO3--N content, urease and protease activity were measured respectively under the conditions of nitrogen fertilizer and no nitrogen fertilizer.[Results]The introduction of Al2(SO4)3 improved the average net mineralization and nitrification rate, with the performance of A0.2S0>A0.1S0, and the mineralization and nitrification gradually decreased with the incubation time. The addition of straw hinders soil nitrogen mineralization and nitrification. After the application of urea, the average net mineralization rate and nitrification rate increased accordingly by 17.34 times and 3.61 times, respectively, after urea application, but it was still inhibitory. The addition of Al2(SO4)3 combined with rice straw (A0.1-0.2S0.6-1) further inhibited the conversion of soil nitrogen. The introduction of Al2(SO4)3 into high quantity rice straw (S>0.6) accelerated the decrease of the decrease in soil NH4+-N and NO3--N was alleviated by the application of nitrogen fertilizer. With the increase of Al2(SO4)3, the contents of ammonium nitrogen and nitrate nitrogen increased, as A0.2S1>A0.2S0.6>A0.1S1. The interaction between Al2(SO4)3 and rice straw had significant effects on urease, protease activity, soil total nitrogen, soil NH4+-N content and soil NO3--N content under the condition of no urea application, and showed extremely significant effects after urea application. There were significant positive correlations between urease and protease activity in soil and total nitrogen content, between NH4+-N and NO3--N, and between net mineralization rate and nitrification rate.[Conclusion]Combined application of Al2(SO4)3 with high rice straw retained more nitrogen from the soil, A0.2S1 treatment had the best nitrogen utilization effect.The research results can provide reference for the improvement and treatment of saline-alkali soil, and provide theoretical support and practical guidance for future research and practice.