The ablation and erosion characteristics of ethylene propylene diene monomer (EPDM) composites under realistic solid rocket motor operating conditions were studied using an ablation motor and an overload simulation erosion motor. Silica fillers and aramid fibers have important effects on the ablation resistance of EPDM composites. The ablation resistance properties of non-silica and non-fiber formulations are obviously poor and worsen under erosion conditions with dense particle jets. From the analysis of the morphology and structure of the composite char layers, the combined use of silica and aramid fibers can make the char layer form a uniform network-like structure with a compact surface and a loose interior, improving both the heat-shielding and erosion-resistance performances of the char layer. By increasing the silica and aramid fiber contents, the erosion resistance performance of EPDM composite was improved under dense particle jet conditions.