Abstract: High performance electromagnetic interference (EMI) shielding materials are urgently needed for the increasing electromagnetic radiation. Heteroatom-doped carbon materials are capable of inducing the generation of electric dipoles through the redistribution of charge density, improving polarisation loss and conduction loss, and enhancing EMI shielding effectiveness (EMI SE). N, S co-doped carbon was prepared by microwave carbonization using methylene blue (MB) as nitrogen, sulphur and carbon source, and multi-walled carbon nanotubes (MWCNTs) as conductive backbone and heating layer, and PVDF nanocomposite film was prepared by composite with polyvinylidene fluoride (PVDF). The effects of the mass ratio of MWCNTs to MB, the thickness of the composite film and the filling amount of N, S co-doped carbon on the shielding performance were investigated. Due to the nanocomposite film's good impedance matching and the EMI shielding mechanism of polarisation and conduction losses, the composite film prepared when the mass ratio of MWCNTs to MB is 1∶1 (Thickness of 0.9 mm, filling amount of 20wt%) had a shielding performance of 43.21-45.20 dB in the X-band (8.2-12.4 GHz). At this point, the hardness and modulus of elasticity of the composite film were measured to be 0.25 GPa and 3.60 GPa, respectively, by a nanoindentation system at a strain rate of 0.05 s⁻¹.