To address the combined demands of impact resistance, thermal protection, and structural support in lunar surface shielding, we developed a multifunctional biomimetic multilayer barrier using a lunar-regolith-simulant-based geopolymer via Direct Ink Writing (DIW). The barrier comprises three bio-inspired tiers: a Bouligand helicoidal layer providing superior impact resistance, a dendritic fractal network integrating thermal insulation with load-bearing capacity, and a honeycomb-like sandwich panel mitigating vibration. Mortise-and-tenon interlocks integrate these tiers into a mechanically robust whole. Mechanical and thermal performance were evaluated through static loading, impact, and insulation experiments, supported by finite element simulations. The Bouligand layer, optimized at a 90° stacking angle, dissipated impact energy through sequential failure, enhancing toughness and resistance to dynamic loading. The dendritic layer, tuned to a 60° branching angle, achieved optimal stability and deformation adaptability, yielding the highest energy absorption and over 60 % thermal insulation effectiveness. The honeycomb base layer outperformed auxetic and chiral counterparts in compressive strength and robustness, while maintaining efficient vibration isolation. Collectively, the integrated architecture demonstrated complementary mechanical and thermal performance, providing multifunctional protection beyond that achievable by conventional single-function layered materials. Under external thermal loads of up to 127°C, the internal temperature remained stabilized near 30°C, confirming excellent thermal shielding. This study clarifies how geometric parameters of biomimetic substructures govern composite barrier responses and establishes an engineering-feasible design paradigm for multifunctional shielding systems, providing theoretical and experimental foundations for lunar infrastructure optimization.