Abstract: The contribution of herbaceous root systems to increase the shear strength of slope soil in open-pit coal mine dumps in alpine regions is examined in this study, and the influence of relevant factors on the shear strength of slope soil is also studied. The dump of the Jiangcang open cast coal mine located in the northern edge of the Qilian Mountains in Qinghai Province is taken as the test area. The mixture of two herbs (Elymus nutans Griseb., Poa pratensis L.) were planted in the slope of the dump and the samples of soil without roots and root-soil composite systems from the dump slope were prepared. The direct shear tests were carried out on the samples. Physical mechanics properties of soil at three different positions of the slope and the relationship between the root number and the shear strength of the root-soil composite systems are analyzed. The results indicate that (1) with the increasing elevation of the dump slope, the density and sand content of the samples of soil without roots and root-soil composite systems significantly increase at the shallow layer of the slope soil, but the content of water, powder and clay decrease significantly. (2) Compared with the samples of soil without roots, the increment amplitudes of the shear strength of the samples of the root-soil composite systems at the slope bottom, slope middle and slope top are 4.09%, 18.92% and 0.69% respectively. (3) In the samples of soil without roots and the root-soil composite systems, the correlation between the moisture content and the cohesion force is significantly negative, with the correlation coefficients (R2) of -0.943 and -0.969, respectively, while the correlation between the content of sand and the internal friction angle is significantly positive, with the correlation coefficients (R2) of 0.940 and 0.926, respectively. (4) Compared with the samples of soil without roots, the increment amplitudes of the cohesion value of the samples of the root-soil composite systems from the slope bottom to the slope top of the dump are 29.23%, 54.40% and 26.45% , respectively.