In order to investigate the changes in soil aggregates due to increased atmospheric nitrogen deposition and its effect on soil water infiltration, two kinds of nitrogen fertilizer ((NH₄)₂SO₄ and KNO₃) with four concentration levels (0, 10, 20, 40 kg/(hm²·a)N)were respectively added in mature and middle-aged coniferous forests at Mount Gongga, aims to investigate the effect of different forms of atmospheric nitrogen deposition on the structure of soil aggregates and the infiltration characteristics of soil water in a subalpine forest. The results showed that: (1) With the increase of nitrogen application, the proportion of large macroaggregate, soil water holding capacity, soil porosity and water stable infiltration rate in middle-aged stands gradually increased; the proportion of large macroaggregate, soil water holding capacity, soil porosity and water stable infiltration rate in mature stands showed a trend of first increasing and then decreasing; (2) The effects of different nitrogen forms on soil aggregate structure, soil porosity and water stable infiltration rate showed no significant difference; (3) Water infiltration was mainly affected by water holding capacity, soil porosity and aggregate formation. Nitrogen addition increased water holding capacity and soil porosity, and enhanced soil aggregation and water infiltration in middle-aged stands.