Abstract: To address the current engineering challenges associated with the lack of design parameters and reference data for Basalt Fiber Reinforced Polymer (BFRP) anchor rods used to support cohesive soil slopes, this study investigates the supporting effect of BFRP anchor rods on complex soil slope engineering. This is achieved through indoor pull-out tests of BFRP anchor rods and in-situ excavation-induced deformation monitoring tests of three types of slopes (unsupported, BFRP anchor rod-supported, and steel bar anchor-supported) conducted at the same site under identical geological conditions. The research findings reveal that compared with unsupported slopes, the design of BFRP anchor rod structures, based on the principle of equal strength replacement of bond strength parameters, can ensure the safety of slope engineering. When compared with slopes supported by steel bar anchor rods, during the entire process of soil slope excavation, slope support installation, and slope immersion leading to instability, the stress and deformation patterns of BFRP anchor rods are similar to those of steel bar anchor rods. However, the axial force of BFRP anchor rods is significantly smaller than the design value, being 30% lower, and the deformation is 10% lower than that of steel bar anchor rods. After immersion-induced failure, the steel bar anchor-supported slope experienced slip failure, while no obvious slip cracks were found in the BFRP anchor-supported slope. This indicates that the reinforcement effect of BFRP anchors on soil slopes is superior to that of steel bar anchors. Based on the structural reliability index value, it is recommended that the minimum safety factor for the pull-out resistance of temporary anchor rod-supported soil slopes with a safety level of Ⅲ be 1.26, which can meet the safety requirements of the anchor rod structure.