Different types of nitrogen (NO3——N, NH4+-N, NO3——NH4+) were studied to see how they affect the activities of nitrate reductase (NR) and glutamine synthetase (GS) in soybean leaves, as well as the protein content in soybean seeds. The results showed that NH4+-N was the most effective in enhancing NR activity, followed by NO3——NH4+ and then NO3——N. All nitrogen types increased GS activity in soybean leaves. Seed protein content was positively correlated with NR and GS activities in leaves. This suggests that selecting soybean plants with high NR and GS activity in leaves can lead to higher protein content in seeds.