The nodulation and nitrogen fixation of major cultivated and wild legumes dispersed over 20 genera. There were 55 species be studied in Alashan desert region. Among them, 15 species have not been reported yet in Allen's "The Leguminoaes". The results showed that 94.8% leguminous plants can nodulate in natural environment. The shapes of nodules of these plants were circular, ellipse or cudgel, and most of them were white, yellow and brown in color. There were 77 samples of nodules be detected with the method of acetylene reduction. There were 24.6% of these nodules samples be ineffective for nitrogen fixation. Activities of nitrogen fixation in nodules varied little, all of them were low, and 45.9% of them be under 1μmol/g·h C 2H 4. The cause of low actions in Alashan desert region were discussed.