Carbon fiber composite core soft aluminum conductors have the advantages of large capacity, small sag, high conductivity, and obvious energy-saving effects, making them one of the ideal solutions to improve the capacity of transmission corridors. However, the bending resistance of carbon fiber composite cores is weak, and they are prone to damage and fracture during installation and construction process, lacking effective detection techniques. In order to solve the above problems, a magnetic leakage detection method of is designed based on the theory of carbon fiber composite core magnetic leakage detection theory. Based on a three-dimensional finite element simulation model of magnetic film coated carbon fiber core, crimping fittings, and excitation device, the influences of key parameters such as permanent magnet size, magnetic pole spacing, and radial air gap distance on magnetic leakage signals are analyzed. The optimized design parameters are: permanent magnet size L₁ is 15 mm, the pole distance L₂ is 50 mm, and the gap distance M is 2 mm. Finally, the influence of the fracture scale of carbon fiber composite material cores on magnetic flux leakage signals is analyzed, confirming the technical feasibility of magnetic leakage detection for local fracture defects in carbon fiber composite cores. The axial component of magnetic induction intensity first increases and then decreases, reaching its maximum value when the fracture scale d=4 mm, while the radial component of magnetic induction intensity increases with the increase of fracture scale.