Soil fungi and actinomycetes, in floodplain wetland on Inner Mongolian Plateau were measured through Spread-Plate-Technique; the divergent characteristics of these two floras at floodplain wetland and typical steppe were analyzed; and several indicators of soil filamentous microbes, for example, diversity, richness, evenness, and dominance, were calculated. For fungi, there is significant difference between enclosed and grazing regions for diversity and richness; and there is significant difference between bump-top in enclosed regions (WT) and bump-top in grazing regions (WJ) for evenness; there is significant difference between in-between-bumps in enclosed regions (FT) and in-between-bumps in grazing regions (FJ) for dominance. For actinomycetes, there is significant difference between in-between-bumps in grazing regions and bump-top in grazing regions for diversity and evenness; and there is significant difference between bump-top and in-between-bumps in enclosed regions , bump-top in grazing regions and in-between-bumps in grazing regions for richness. The dominant groups are Mucor, Penicilliu floodplain wetland. But the dominant groups have changed in enclosed and grazing regions. The results have demonstrated a better understanding toward the development and succession mechanisms of floodplain wetland to provide the basis for protection and rational utilizations of floodplain wetland.