Polypropylene laminated paper (PPLP) is an important type of insulating material used in High-temperature superconducting (HTS) cables. However, partial discharge (PD) is found to be a key indicator to reveal the state of the insulation system. During the operation of HTS cable, PPLP insulation material is vulnerable to the combined effect of electrical, thermal and mechanical stress, resulting in insulation aging, cracking and even insulation failure. In order to analyze the damage mechanism of insulation materials caused by cavity discharge from the micro perspective and atomic level, molecular simulation technology was introduced. In this paper, the micro-reaction of molecular model under electric field was simulated based on Materials Studio DMol3/Dynamics module, and the changes of molecular energy under different external electric fields were studied. Meanwhile, the cellulose molecular motion and pyrolysis of PPLP surface insulation paper were explored, and the microscopic reaction mechanism was revealed from the atomic level. The results show that: (1) The LUMO-HOMO energy gap can be used to represent the structural stability between molecules. The larger the electric field is, the smaller the LUMO-HOMO energy gap is; (2) The outer insulation paper cellulose (C-O-C) bond breaks under the impact of high energy electrons, and the intermolecular force decreases; (3) Cellulose molecular decomposition products include CO2, CO, CHO2，C2H4O2 and small molecule free radicals. This paper reveals the damage mechanism of PPLP from the micro perspective, which has potential application value in the fault diagnosis of superconducting cables.

Cellulose;degradation;Molecular Dynamics