EPDM composites by intercalation are usually used as the sealing materials of especial containers because of its excellent aging and sealing properties. By using the seal structure containing O-ring, the sealing properties of the O-ring of EPDM intercalation composites in high temperature were studied by means of mass spectrometer of leak detection and pressure observation. The result shows that the O-ring seal of EPDM intercalation composites has excellent sealing properties below 152 ℃,and its apparent leakage rate is no more than 1×10-7 Pa·m3/s.