This study adopts a solvent-free in-situ molding process, using liquid ethylene-propylene-diene monomer (LEPDM) as the base rubber to prepare vacuum sealing materials. The effects of the blending ratio of EPDM/LEPDM on mechanical properties, processing characteristics, physical-mechanical properties, compression characteristics, and vacuum condensable volatiles were investigated. The influence of lamellar intercalated structural fillers on gas permeability was also examined. The results indicate that the addition of LEPDM significantly reduces the Mooney viscosity, improves filler dispersion, and achieves good processability. When the LEPDM blending amount exceeds 20 phr, significant changes occur in mechanical properties, compression modulus, and compression set, which are related to phase transformation. Vacuum pretreatment and vacuum condensable volatile test results show that the traditional plasticizer DOP exhibits high total mass loss (TML) and collected volatile condensable materials (CVCM). However, when LEPDM is partially used to replace EPDM at a blending ratio of 20 phr, TML ≤ 1% and CVCM ≤ 0.1% can be achieved. With the increase in organically modified montmorillonite (OMMT) content, the gas permeability coefficient first decreases and then increases. When the OMMT content is 15 phr, the material exhibits good gas barrier properties