The nodulation and nitrogen fixation of 53 species belonging to 24 genera major cultivated or wild legumes are studied in Gansu-Ningxia region of the loess plateau. There were 87 strains of root nodule bacterial from 112 samples be separated, and 63.5% of those nodules samples be effective for nitrogen fixation. The activities of nitrogen fixation in nodules of various species varied greatly and all of them were low that 35% of them are under 1 μmol/(g·h) C\-2H\-4 and more than 10 μmol/(g·h)C 2H 4 is only 6%. The characteristics of symbiotic nitrogen fixation and action of soil and water conservation in environment were discussed.