Abstract: Due to high temperature and neutron irradiation, the performance of insulation material in nuclear reactor is significantly degraded. It must be replaced after a period of time. In order to extend the life of insulation material under normal operation of the nuclear reactor, it is necessary to study the irradiation performance. In the work, the fiber cloths from Qinshan Nuclear Power Plant were irradiated with different doses. The irradiation equipment with temperature control was designed and completed in order to ensure irradiation temperature as set temperature. The effect of temperature on tensile property of un-irradiated insulation material was studied. The mechanical property has different degrees of decline under high temperature. By using of SEM, the effects of irradiation on structure and composition were also studied. The results show that the composition and microstructure of insulation material have no significant change, but microstructures are different among samples under different conditions.