The aging property of the rubber compound of insulation layer determined the storage time before the use of the insulation layer. In order to grasp the influence of the storage time of the rubber compound of insulation layer on the subsequent performance of the insulation layer， the storage time of the rubber compound of insulation layer was controlled.The thermal oxygen aging test was used to study the change of properties of the rubber compound of insulation layer after different aging time. The results show that， with the extension of the aging time， the DCP decomposes and the molecular chain of EPDM breaks at high temperature， the mechanical properties， vulcanization properties， adhesive properties and gel content of the rubber compound of insulation layer decreases， while other physicochemical properties do not change significantly. Therefore， in order to effectively improve the storage period of the insulation layer at high temperature and extend the service life， the strict attention should be paid to storage temperature and keeping away from light and ultraviolet radiation.