Abstract: This paper proposes a novel design methodology for E-plane waveguide bandpass filters (BPF) based on double-layer grounded spoof surface plasmon polaritons (DLG-SSPP). The DLG-SSPP unit cell features two distinct metallic patterns printed on both sides of a single-layer dielectric substrate, interconnected through metallic via holes. By simplifying the equivalent circuit model of the complex artificial SSPP structure, the filtering performance and dispersion characteristics of DLG-SSPP are systematically investigated. The simplified model facilitates theoretical design of the SSPP dispersion curves and guides structural optimization of the unit cell, thereby enabling rapid design and performance prediction for E-plane waveguide BPF. To validate the proposed methodology, two DLG-SSPP-based waveguide BPFs are analyzed, designed, fabricated, and experimentally characterized. Measurement results demonstrate that both filters exhibit low insertion losses and compact footprints, indicating promising potential for wireless communication applications.