Abstract: In this paper, basalt fiber (BF) was used as reinforcement phase and polypropylene (PP) as the matrix, BF/PP foam composites were prepared using a chemical foaming secondary mold opening process. The thermal properties, rheological properties, foaming behavior and mechanical properties of BF/PP foam composites modified with different sub structure coupling agents were studied using DSC, SEM and other characterization techniques. The results show that after modifying BF with different molecular structure coupling agents, the crystallization and rheological properties of the composite improve, the crystallinity increase, and the melt viscoelasticity improve. When KH-550 is used to modify BF, the foaming quality of BF/PP foamed composites is the best, with a foam cell size of 84.52 μm. Cell density is 2.45×10⁵ cells/cm³. After BF is modified by coupling agent, the flexural strength, flexural modulus, and tensile strength of the foam composite are improved compared to those of the unmodified BF; When modifying BF with KH-792, the maximum flexural strength, flexural modulus, and tensile strength are 33.4 MPa, 1919 MPa, and 21.4 MPa, respectively. This study provides a theoretical reference for the development and industrial application of BF/PP foam composite materials.