Interrelationships between plants are affected establishment and survival, as a result, knowledge of how these relationships occur can be used for the maintenance of species and improvement and management of rangelands. This study was conducted to evaluate the effect of Astragalus microcephalus on index vegetation under the canopy in semi-steppe rangeland of protected area in Tange-sayad. For this purpose, percentage of vegetation cover under the canopy of this species and its open space adjacent was measured using a flexible plot along the 100 meters transect. The results showed that 30 species under the canopy of Astragalus microcephalus and 33 plant species in the open space adjacent. In the under canopy of Astragalus microcephalus 6 exclusive species such as Chaerophyllum macropodum, Onobrychis gaubae, Salvia ceratophila, Stachys pilifera and Artemisia aucheri existed that mostly related to perennial, palatable and pharmaceutical plants. In contrast, open space exist 9 exclusive species including Centaurea virgata, Hypecum pendulum, Clypeola aspera, Roemeria refrecta and Xeranthemum annum that mostly related to invasive and annuals species plant. Generally, the vegetation index under canopy of Astragalus microcephalus due to moderate grazing livestock in the region less affected to mechanical facilitating of Astragalus microcephalus but the facilitating role of Astragalus microcephalus in preserving of valuable plant species is highly visible.