Abstract: Mesophase pitch-based C/C composites, which offer advantages such as low density, high thermal conductivity, high specific modulus, and low coefficient of thermal expansion, are candidate materials for heat radiator fins in space heat-pipe reactors. Since space heat-pipe reactor design requires joining C/C composites to metal thermal components, brazing Cu to C/C composites has become a critical technical pathway for manufacturing high-performance fins. As the reinforcement phase and thermal conduction pathway in composites, fiber orientation significantly influences material properties, imparting pronounced anisotropy to characteristics such as thermal conductivity, coefficient of thermal expansion, and tensile strength. Thus, variations in fiber orientation within composites will inevitably affect joint performance. To address this objective, this study employed highly stable commercial AgCuTi filler metal to braze C/C composites with different fiber orientations to Cu metal. The microstructure, room temperature shear strength, fracture morphology, and thermal conduction properties of the brazed joints were systematically investigated. The results indicate that joints with fibers oriented perpendicular to the brazing surface (C/C⊥-Cu) exhibit the best performance. Under the condition of 880 °C and without applied pressure, the room temperature shear strength reached 33.19 MPa (peak strength of 41.65 MPa), and the thermal diffusivity measured 154.539 mm²/s. In contrast, joints with fibers parallel to the brazing surface (C/C//-Cu) demonstrate inferior performance, with a significantly lower room temperature shear strength of only 14.71 MPa and a reduced thermal diffusivity of 84.581 mm²/s. Microstructural and fractographic analysis reveals that the brazed joints formed under this process can effectively absorb external loads due to the presence of highly plastic and dense Ag-based and Cu-based solid solutions. Concurrently, a continuous TiC layer formed on the C/C composite side ensures stable heterogeneous bonding between the metal and the C/C composite. The C/C⊥-Cu joint exhibits significantly superior strength to the C/C//-Cu joint. This difference stems from their distinct failure mechanisms: When subjected to shear stress perpendicular to the fiber orientation, the C/C⊥-Cu joint experiences crack propagation primarily within the TiC layer at the joint interface, as the fibers themselves possess higher shear resistance than the joint region. In contrast, the C/C//-Cu joint fails differently under stress parallel to the fiber direction. Cracks tend to initiate and propagate along interlaminar regions or between fiber bundles within the composite material. For 1D or 2D composites, interlaminar shear strength is typically lower than in-plane shear strength, making the C/C⊥-Cu joint more resistant to shear failure. Furthermore, braze filler infiltration provides additional pinning effects that enhance joint strength. The C/C⊥-Cu configuration facilitates better braze penetration, contributing to its higher shear strength. The C/C⊥-Cu joint exhibits both ideal mechanical properties and thermal conductivity, showing promise for use in brazing heat radiator fins for space heat-pipe reactors.