In order to resolve the issue of soil degradation in the dumping site of open-pit coal mine in arid area, the effects of actinomycetes on the root growth and rhizosphere soil fertility of onobrychis viciaefolia in the dumping site of Xinjiang Heishan Open-pit Coal Mine were investigated by highly efficient actinomycete inoculation and in-situ pot experiment. The results show that: (1) Under the drought conditions, actinomycetes inoculation could significantly promote the development of root morphology and the growth of onobrychis viciaefolia. Compared with the control without actinomycetes inoculation, the total root length, average root diameter, root surface area and total root volume of onobrychis viciaefolia were significantly increased (P<0.05), and the fresh weight of root and stem leaf and the total fresh weight were increased by 77.24%, 130% and 103.49% respectively. (2) Actinomycetes inoculation significantly enhanced the drought resistance of onobrychis viciaefolia. Meanwhile, the root glutathione, proline content and root activity were increased by 35.36%, 229.23% and 363.75% respectively, while malondialdehyde content and the permeability of the root cytoplasmic membrane were reduced. (3) Actinomycetes inoculation significantly improved the rhizosphere soil fertility ofonobrychis viciaefolia. Specifically, the colonization amount of actinomycetes for test in rhizosphere soil of onobrychis viciaefolia is 2.5 × 10⁵ cfu/g. The total number of soil bacteria and actinomycetes in the rhizosphere were increased by 113.7% and 563.64% respectively. Besides, the activities of soil polyphenol oxidase, urease and alkaline phosphatase were significantly increased (P<0.05) by comparison with the control. Thus, the contents of total nitrogen, available phosphorus and available potassium in rhizosphere soil were significantly increased by actinomycetes, of which the total nitrogen reached the largest increase rate. (4) Correlation analysis shows that root biomass of onobrychis viciaefolia was significantly and positively correlated with the quantity of soil bacteria and actinobacteria, the activity of urease and alkaline phosphatase, and the total nitrogen (P<0.01). These results also verify that actinomycetes inoculation in soil could enhance the drought resistance of plant, increase the number of microorganisms, enzyme activity and fertility in rhizosphere soil, and significantly promote the development and growth of plant root, thus providing scientific basis for vegetation restoration and degraded soil improvement in arid coal mining areas.