Abstract: Salt and alkali stress has adverse effects on soybean plant growth and nitrogen absorption, which seriously affects soybean yield. Exogenous application of Trichoderma fertilizer is an effective way to alleviate the effect of salt and alkali stress on soybean. Therefore, in order to clarify the effect mechanism of Trichoderma on nitrogen metabolism of soybean seedlings under saline-alkali stress. In this experiment, the saline-tolerant cultivar Hefeng 50（HF50） and saline-alkali sensitive cultivar Kenfeng 16（KF16） were selected as test materials. Pot culture was carried out in saline-alkali soil, and 200 mL of spores of Trichoderma harzianum, Trichoderma asperellum and the Trichoderma mixture, 1×10~9 spores·L^-1 per liter of soil were poured into the soil. Chloroplast ATP ase synthesis, nitrogen metabolism and other physiological and biochemical indexes of soybean seedlings were determined. The results showed that, salt and alkali stress significantly increased NH■ content in soybean seedlings, resulting in ammonia toxicity, while application of different trichoderma fertilizers significantly decreased NH₄⁺ content in KF16 and HF50 soybean leaves. The decreases were 38.31%, 41.56%, 63.62%（KF16） and 20.55%, 25.58%, 55.62%（HF50）, respectively. Compared with the control treatment, the activities of Ca²⁺-ATPase and Mg²⁺-ATPase in soybean leaves were significantly increased by 36.15%-5.22%（KF16）, 28.51%-62.47%（HF50）, 23.09%-62.58%（KF16）, and 14.37%-44.10%（HF50）, and then promoted the photosynthetic rate of leaves to provide more raw materials and energy for the nitrogen metabolism of soybean seedlings, and then improved the nitrogen metabolic activity of soybean. In conclusion, the different Trichoderma treatments could effectively alleviate the damage caused by saline-alkali stress on soybean and promote its growth.