The interfacial pressure of the cable intermediate joint is a vital factor influencing its insulation performance. The interfacial pressure inevitably decreases with the aging of ethylene propylene diene monomer (EPDM) rubber. In order to study the evolution of interfacial pressure, this paper established an accelerated aging experimental platform at 100 ℃, 125 ℃, and 150 ℃ for different aging times to carry out thermal-mechanical aging experiments on EPDM rubber. The evolution of the interfacial pressure was also analyzed by the finite element analysis combined with the real working conditions and aging factors such as electrical, thermal, and mechanical stresses. The results showed that the mechanical properties of EPDM rubber were gradually degraded and the interfacial pressure gradually decreased during the thermal-mechanical aging process. The performance deteriorated faster with increasing aging temperature. The interfacial pressure decreased from 0.172 MPa to 0.123 MPa after aging at 150 ℃ for 720 h, closing to 0.1 MPa which was considered the lowest limit of the installation requirement. The results of the study provide a theoretical basis for the stable working of the EPDM rubber cable intermediate joint.