Context <p>Polyimide (PI) is a key arc-resistant material, yet its molecular-level degradation under fault-arc plasma remains unclear. Here, arc-ablation experiments were combined with multi-scale simulations to elucidate its decomposition pathways. FTIR results indicate that high-energy plasma particles exceed the maximum bond dissociation energy of PI, causing highly disordered scission distinct from thermal decomposition. Bond-order and BDE analyses were used to identify vulnerable sites, followed by ReaxFF/ZBL molecular dynamics and Fukui function analysis to probe reaction pathways. The results show that C–C and N–C bonds between imide and phenyl rings, as well as aromatic ether C–O–C linkages, are the most susceptible to cleavage. Nitrogen atoms display strong nucleophilicity, inducing C–N bond rupture and ring opening; the resulting formation of additional N–H groups explains the intensified and broadened N–H bands in the FTIR spectra. In contrast, electrophilic oxygen preferentially attacks aromatic ether bonds, generating short-chain fragments that drive rapid mass loss. These consistent experimental and computational insights establish an atomic-scale path of PI degradation under arc plasma.</p> Methods <p>The modeling process was carried out using BIOVIA Materials Studio. Lmp2arc was used to convert .car files to .data files. The calculations for the polyimide bond order were performed using the DMol3 module of Materials Studio, with LDA-PWC selected for the generalization. This paper employs a hybrid ReaxFF and ZBL force field in LAMMPS to simulate ion bombardment of the PI surface (including the atoms) in an electric arc. Gaussian 16.0 was utilized to optimize the geometry at the B3LYP/6-31G(d,p) level. Fukui function calculations were performed for polyimide using Multiwfn, based on the electron wave function generated by Gaussian 16.0.</p>