Abstract: The study with fuzzy set ordination (FSO) showed that in the National Nature Res erve in Yellow River Delta, there was a greater difference in plant habitat and vegetation type along a water table depth gradient. At the place with 40 cm to -30 cm water table depth,a transitional belt from water body to land,xerophiles and hydrophytes coexisted, plant species were most abundant, and vegetation cove rage was the largest. At the place of -30 cm to -50 cm water table depth, soil s a linization and alkalization had the highest degree because of the lower ground w ater level, while at the place with ＜-50 cm water table depth, soil surface was relatively dry, salinization and alkalization had a lower degree, and drought-tolerant vegetation took dominant place. Water table depth gradient had significa nt effects on soil moisture and air condition and soil physical, chemical and biological processes, and accordingly, affected the spatial distribution and ecological characters of the vegetations in the test region.

Key words: Ailao Mountain, Disturbances, Soil inorganic nitrogen, Middle mountain moist evergreen broadleaf forest