Abstract: The infiltration and subsequent degradation by molten calcium-magnesium-alumina-silicate (CMAS) at elevated operating temperatures remain a critical challenge leading to the premature failure of thermal barrier coatings (TBCs) in advanced aero-engines. Consequently, regulating the coating microstructure to physically block CMAS intrusion has emerged as a core strategy for enhancing coating durability. Focusing on the Porous Embedded Particle Clusters (PEPC) structure, which exhibits exceptional potential for CMAS resistance, this study aims to systematically investigate the infiltration dynamics of molten CMAS. A coupled numerical model combining two-dimensional creeping flow and particle tracing was established to elucidate the underlying mechanism by which particle geometric characteristics within flat fusiform pores affect CMAS infiltration. The simulation results indicate that at the dual-particle scale, the synergistic coupling of large particles and micro-spacing significantly amplifies the pore-throat throttling effect. Meanwhile, arranging particles perpendicular to the flow direction effectively eliminates the hydrodynamic shielding effect, thereby maximizing the blocking efficiency. At the multi-particle scale, the average particle spacing is identified as the dominant factor governing the anti-infiltration performance. A non-linear threshold control mechanism was revealed, pinpointing a critical spacing value of approximately 0.7 μm in PEPC structures with 72% porosity, below which the infiltration resistance improves drastically. Furthermore, this study clarifies a strong coupled blocking mechanism among particle spacing, porosity, and pore tortuosity. It is found that increasing the proportion of small particles achieves a dual-blocking effect by simultaneously reducing the average spacing and elevating the tortuosity of the flow channels. Ultimately, these findings clarify the physical essence of infiltration mitigation in PEPC structures, providing a robust theoretical foundation for the microstructural optimization of next-generation high-performance TBCs.