The nodulation and nitrogen-fixing resources of legumes plants from 31 counties of Gansu province were investigated;meanwhile the corresponding rhizobia were isolated. The 31 counties belong to Qingyang,Pingliang,Baiyin,Lanzhou,Linxia,Dingxi,Tianshui,Gannan and Longnan. In total,790 strains were isolated from 800 nodule samples,whose hosts belong to 34 genera,82 species or varieties. These nodules are mainly round,ellipse and coralloid in shape,pink and yellow in color,with size ranging from 1 mm to 10 mm. The shape is determined by meristem,if it has meristem,it will be ellipse and coralloid (if not,it will be round. The color of the nodules are decided by legohomoglobin,which is very important in the process of nitrogen-fixing. It is found that the shape, size and color of nodules are similar among different species,which belong to the same genus,but there are great differences if these nodules belong to different genera. The color,shape and size are deeply affected by soil condition. In addition the relationship between the distribution of rhizobia and the natural factors is very close,namely soil moisture,soil temperature and elevation. To some extent,the distribution of legumes and their associated plants show some principle,the legumes almost live in the place with enough light, moisture and nutrition. The diversity of associated plants is relatively limited,and the number is limited. Additionally,it is found that many legumes are used in soil and water conservation,in preventing the soil from desertification.