By taking the composite of the roots of Sabina vulgaris and soil around the roots as a research object,the effects of different root diameter classes and root layouts on shear performance of the root-soil composite were investigated through laboratory shear tests.Results showed that under different normal stresses,shear strength for the root—soil composite with roots was significantly greater than that for the disturbed soil without root.As for the root—soil composite,shear strength contributed by vertical roots was greater than that by horizontal roots.Under the condition of the same number of roots contained,shear strength for the composite was not proportional to the size of root diameter,but presented an increasing—fallback—rebounding trend with the increased root diameter.The study may provide some technical parameters and a theoretical support for the future plantation of Sabina vulgaris as a soil and water conservation measure.