The study investigates the fabrication and properties of accordion-shaped Co/Co3O4@N-doped carbon nanosheets (Co/Co3O4@NC) with gradient magnetic heterointerfaces. These nanosheets were synthesized through a high-temperature carbonization and low-temperature oxidation process. The experimental and theoretical results indicate that the gradient magnetic heterointerfaces, which include magnetic-heteroatomic components, optimize impedance matching and enhance electromagnetic wave absorption. Specifically, the Co3O4 domains on local Co nanoparticles adjust the magnetic-heteroatomic components, improving interfacial polarization and magnetic coupling. The Co/Co3O4@NC nanosheets exhibit strong electromagnetic wave attenuation capabilities, achieving a minimum reflection loss of −53.5 dB at a thickness of 3.0 mm and an effective absorption bandwidth of 5.36 GHz. This work provides a new approach to optimizing electromagnetic wave absorption by engineering magnetic heterointerfaces.The study investigates the fabrication and properties of accordion-shaped Co/Co3O4@N-doped carbon nanosheets (Co/Co3O4@NC) with gradient magnetic heterointerfaces. These nanosheets were synthesized through a high-temperature carbonization and low-temperature oxidation process. The experimental and theoretical results indicate that the gradient magnetic heterointerfaces, which include magnetic-heteroatomic components, optimize impedance matching and enhance electromagnetic wave absorption. Specifically, the Co3O4 domains on local Co nanoparticles adjust the magnetic-heteroatomic components, improving interfacial polarization and magnetic coupling. The Co/Co3O4@NC nanosheets exhibit strong electromagnetic wave attenuation capabilities, achieving a minimum reflection loss of −53.5 dB at a thickness of 3.0 mm and an effective absorption bandwidth of 5.36 GHz. This work provides a new approach to optimizing electromagnetic wave absorption by engineering magnetic heterointerfaces.