Abstract: We studied the effects of polyacrylamide (PAM) and the grass root system on the shear strength and physical properties of purple soil on barren slopes. Three different treatments were applied to purple soil on barren slopes: PAM (single application of PAM), grass (single planting of grasses), and grass+PAM. The root parameters were measured using the WinRHIZO (Pro.2004c) root analysis system and soil shear strength of soil samples was determined using a ZJ-type strain-controlled direct shear apparatus. We also determined the basic physical properties of soil samples. The main results were as follows: 1) All three treatments significantly improved the soil water holding capacity. The grass+PAM treatment had the best effects on soil porosity and water content, followed by the grass treatment. 2) All three treatments significantly increased the abundance of microaggregates in the 1-0.25 mm and 0.25-0.05 mm size ranges, and decreased the abundance of those in the smaller size category (<0.01 mm). 3) The average internal friction angle of grass was 37.12% and 36.59% higher in the grass and grass+PAM treatments, respectively, than in the control, and the average soil cohesion in the grass and grass+PAM treatments was increased by 69.47% and 83.64%, respectively. The root surface area density and abundance of roots with diameter between 0.7 mm and 0.9 mm were the main factors affecting the shear properties of soil. 4) The growth of grass roots was markedly affected by PAM, which increased the average root length density, root surface area density, root volume density, and root weight density of Cynodon dactylon soil samples by 15.57%-53.16%, and of Trifolium repens soil samples by 23.02%-80.00%.