Ethylene propylene diene monomer (EPDM) rubber is widely used as sealing material for valve cooling system of converter station in DC transmission engineering due to its excellent properties. However, various factors, including temperature, humidity and oxygen, would lead to performance degradation. In this paper, the effects of vulcanization systems on the vulcanization characteristics, mechanical properties and damp-heat aging properties of EPDM rubber were studied. The results showed that the conventional sulfur vulcanization (CV), effective vulcanization (EV), and semi-effective vulcanization (SEV) systems exhibited relatively high vulcanization efficiency. The mixed vulcanization (MV) system had comprehensive optimal mechanical properties. After damp heat aging, the tensile strength and elongation at break of EPDM rubber in CV and peroxide vulcanization (DV) systems decreased but their hardness increased to some extent. Owing to the stable cross-linked structure of EV and SEV systems, their mechanical properties only slightly changed. The change of the mechanical properties of MV system was similar to that of CV system, but the change range was small.