With the explosive growth of intelligent devices, low-cost multifunctional materials will be in great demand in the near future. Preparation of flexible polymer composites from waste plastics can not only reduce the production cost but also alleviate the environmental concern. Herein, the thermoplastic polymers from waste cross-linked polyethylene (CLPE) cables were efficiently recycled by partially breaking the cross-linking points in the solid state and, thus, fully utilized in the low-cost, high-strength, and allweather electromagnetic interference (EMI) shielding materials. Briefly, with the assistance of the homemade solid-state shear milling (S3M) reactor, the waste CLPE cables were converted into fine micropowders at a large scale. The obtained decross-linked CLPE powders were coated with carbon nanotubes (CNTs), and then the coated complex particles were compacted together during the microwave sintering process. In this way, the segregated structure with CNTs selectively enriched at the interfaces of the CLPE phases was successfully constructed by taking full advantage of the selective heating mode of the microwave and the remaining crosslinked structure in CLPE. The sintered CLPE/CNTs containing 7.0 wt % CNTs exhibit an electrical conductivity of 22.6 S/m and an EMI shielding effectiveness (EMI SE) of 35.0 dB, respectively. More importantly, the resulting composite shows superior stability in electrical and EMI shielding properties even under extreme conditions, such as acid/alkali solution soaking and repeated bending deformation. The segregated CLPE/CNT composite also shows excellent mechanical properties with tensile strength above 20 MPa and elongation at a break of 280%. This interfacial engineering strategy offers an effective method to convert the unrecyclable waste plastic into value-added materials, showing great significance in resource recycling utilization.