“Intermediate phase pitch based carbon fiber (MPCF) has shown great potential in the field of spacecraft structural materials, but its highly graphitized surface and strong chemical inertness result in weak bonding with the resin matrix interface, severely restricting the overall performance of composite materials. To address this issue, researchers have conducted research on the characterization and modification of interfacial mechanical properties of MPCF/epoxy resin composites. The precise quantification of interfacial shear strength (IFSS) was achieved through nanoindentation technology for single fiber ejection testing of MPCF. On this basis, polydopamine (PDA) was used as the binder and carbon nanotubes (CNTs) as the reinforcing phase to modify the surface of MPCF by sizing, and a hierarchical reinforcement interface with micro nano structure was constructed. The research results show that when the content of CNTs is 0.1% of PDA mass, CNTs have the best modification effect on MPCF. A uniform CNT network is formed on the surface of MPCF, and the surface roughness is significantly increased. Oxygen and nitrogen functional groups are successfully introduced, and the contact angle with epoxy resin is reduced from 64 ° without modification to 48 °. The interface mechanical performance test results showed that after the synergistic modification of CNTs/PDA, the IFSS of the composite material increased from 17.8 MPa without modification to 24.4 MPa, an increase of 37.1%. This is mainly attributed to the synergistic effect of the micro mechanical locking effect constructed by CNTs and the chemical bonding introduced by PDA, which significantly improves the wettability of epoxy resin to MPCF.”