In this study, the composition of dominant microorganisms, such as fungi and actinomycetes, in river wetland soil on typical steppe were measured through Spread-Plate-Technique; the divergent characteristics of these two floras at river wetland and typical steppe were analyzed; and several indicators of soil filamentous microorganisms, for example, diversity, richness, evenness, and dominance, were calculated. The results demonstrated that there is obvious divergence characteristics of terrestrial distribution for predominant flora, i.e. soil filamentous microorganisms, at river wetland on typical steppe. For fungi, there is significant difference between river center (HX), riverside (HB), low floodplain (DQ) & high floodplain (EQ), and typical steppe (DT) for diversity and richness; and there is significant difference between HX and DQ & EQ for evenness. For actinomycetes, there is significant difference between HX & HB, and EQ & DT for diversity and evenness; and there is significant difference between HX, HB, DQ & EQ, and DT for richness. There are certain differences between predominant floras at river wetland and typical steppe. At HX, the most dominant flora is Mucor to account for 100%. At DQ, the dominant floras are Mucor, accounting for 50%, and Cephalosporium, accounting for 50%. At EQ, Mucor accounts for 62.2% and Cephalosporium accounts for 21.1%. At DT, Penicillium has become the dominant flora to account for 69.2%. For actinomycetes, balding group accounts for 100% at HB and 66.7%. At DQ, two dominant floras are balding group and Griseofuscus to account for 38.5% and 41.3%, correspondingly. At DT, the dominant flora is Griseofuscus to account for 61.7%. For filamentous microorganisms at river wetland, two indicators, numbers and diversity, have shown the divergent characteristics that it evolves from humidogene to humidogene﹢terrestrial, then to terrestrial, where soil environment at DQ, EQ and DT are more suitable for the growth of filamentous microorganisms, and the decomposing processes from filamentous microorganisms have facilitated the development and succession process of river wetland. The results have demonstrated a better understanding toward the development and succession mechanisms of river wetland to provide the basis for protection and rational utilizations of river wetland.