Structural and Functional Integration of High‐Modulus Carbon Fiber Composites Enabled by Continuous Fiber 3D Printing and SiC Interfacial Networks

High‐modulus carbon fiber/epoxy resin (HMCF/EP) composites are promising lightweight materials for critical components in new energy vehicles. However, their practical use is hindered by brittle‐fiber processability, weak interfaces, and insufficient multifunctional integration. Here, a nano‐SiC regulated in situ 3D printing strategy is developed to fabricate sandwich‐structured HMCF/SiC/EP composites. During continuous deposition, SiC nanoparticles are selectively enriched at fiber and EP interfacial gaps. This interfacial enrichment densifies the interphase, suppresses void formation, bridges adjacent fibers, and constructs coupled pathways for thermal transport and electromagnetic attenuation. The optimized composite with 5 wt.% SiC achieves a flexural strength of 784.2 MPa and an interlaminar shear strength of 63.2 MPa, corresponding to improvements of 34.8% and 17%. The in‐plane thermal conductivity reaches 33.65 W/(m K), which is 66% higher than that of the unmodified composite. Meanwhile, the through‐plane thermal conductivity reaches 1.27 W/(m K), showing a remarkable 354% enhancement. The X‐band electromagnetic interference (EMI) shielding effectiveness reaches 56.44 dB, a 241% improvement. These results identify targeted interfacial enrichment as a decisive factor in resolving the structure–function incompatibility of brittle continuous fiber composites beyond indiscriminate filler loading. These results demonstrate a potential interfacial engineering strategy for additive manufacturing of lightweight multifunctional composites with enhanced mechanical, thermal management, and EMI shielding capabilities.