This paper employs a dynamic vulcanization two-step extrusion process to prepare ethylene propylene diene monomer (EPDM)/high-density polyethylene (HDPE) thermoplastic vulcanizate (TPV). It investigates the influence of different rubber-plastic ratios on the mechanical properties and microstructure of EPDM/HDPE-based TPV, and analyzes the impact of varying amounts of crosslinking agents on the processing properties of EPDM/HDPE blends. The results indicate that as the resin content decreases, the tensile strength and elongation at break of the TPV show a significant decreasing trend. When the rubber-plastic ratio is 60/40, it exhibits superior mechanical properties and a distinct "sea-island" structure in its microstructure, which is superior to other rubber-plastic ratios upon comprehensive comparison. As the amount of crosslinking agent increases, the crosslinking rate gradually accelerates. However, an excessively high crosslinking rate makes it difficult to achieve the requirements of phase inversion and fine rubber crushing. When the amount of crosslinking agent is 0.3 parts, the crosslinking rate is moderate, resulting in a TPV product with good surface smoothness and uniform texture distribution.