Root-soil composites of four desert plants and pure soil were investigated by fast-shear test using direct shear apparatus to explore shear strengths of root—soil composites and the impacts of root diameter and vertical pressure on shear strength. Results showed that shear strengths of the root—soil composites for Caragana microphylla Lam.,Salix psammophila,Sabina valgaris Ant.,and Artemisia sphaerocephala Krasch. are higher than shear strength of pure soil within 1.5 m shallow layer(25 kPa). Equivalent friction angles of the root—soil composites do not change obviously as compared with pure soil. For the same diameter (1.25 mm),cohesive forces of the root—soil composites are greater than pure soil and the range of increased cohesion is 4.60%～46.23% and by the cohesion,the order of the plants is Caragana microphylla Lam.Sabina valgaris Ant.Salix psammophilaArtemisia sphaerocephala Krasch.. Shear strengths of the composites are increased to different extents when root diameter is increased.