Abstract: To investigate the quantitative influence of vegetation roots on the erosion characteristics of the river bank under field conditions, an erosion test device was designed, and 18 groups of in-situ tests of critical shear stress and erodibility coefficient were carried out. Four typical locations in the upper reaches of the Tarim River and four typical vegetation roots were selected, including Populus euphratica (PE), Phragmites australis (PA), Tamarix ramosissima (TR), and Alhagi sparsifolia (AS). According to the experimental results, the critical shear stress of the soil basically increases as a power function with the increase in root content. Among the four studied vegetation roots, the TR roots exhibited the largest critical shear stress at the same root content, followed by PE and AS, while the PA roots exhibited the smallest value. The increased effects of the critical shear stress with unit root content increase for the four vegetation species were analysed. The order was AS > PE > TR > PA. The quantitative relationship between the critical shear stress and root volume density was established. The existence of roots can reduce the soil erodibility coefficient. It decreases with the increase in root content. With the increase in unit root content, the order of the decreased effects of the erodibility coefficient for the four vegetation species was AS > PE > TR > PA. Based on in-situ test results, the power function relationships between the soil erodibility coefficient and critical shear stress were obtained with and without root influence, and compared to existing experimental results. The experimental results in this study are consistent with the existing studies, except that the corresponding coefficients and exponents are different. This study can provide a reference for riverbank protection by vegetation roots and calculation of the bank erosion process in the Tarim River.