At present, the aging state evaluation of EPDM used as the insulation of power cables mainly focuses on the single stress or electrical and thermal stresses. There are very few studies on the effect of mechanical stress on the insulation of power cables. Therefore this paper studies the dielectric properties of EPDM suffering electrical, thermal and tension stresses. This paper tests the polarization and depolarization current under different aging conditions, and extracts the aging factor A to characterize the insulation performance and aging state of EPDM. Experiments show that a short time of aging does not cause insulation deterioration, and the insulation began to deteriorate after 20 days of aging at 120 °C. Tensile stress accelerates the process of insulation deterioration, and the polarization depolarization current and aging factor A of 1.6  are greater than that of 1.0. Compared to tensile stress, electrical stress has a greater effect on insulation deterioration.