In order to study the breaking mechanism of 10 kV overhead insulated lines by lightning, an ablation model of insulated conductors is established based on COMSOL, and the ablation status of the conductors when suffering lightning current and power frequency short?circuit current is simulated respectively. Then the force model of the conductor is established to analyze the conductor force when ablating. Simulation results indicate that, the lightning current only leads to one perforation on the conductor insulation layer. The power frequency arc can ablate and fuse the insulated wire in 1.3 s without considering the effect of external forces. The mechanical simulation results of the insulated conductor show that the tension of the conductor suffers abrupt changes at the ablation site, and the electromotive force between the wires and the electromagnetic thrust of the arc act on this site. Combined with theoretical analysis, it is concluded that the main reason for the line breakage caused by lightning is the combined action of heat and mechanics, which results in plastic deformation and brittle fracture. The simulation research provides a reference for lightning protection of 10 kV overhead insulated conductors.