Abstract: In this study, a novel double-layer flexible protective gear was proposed based on the multi-level structure of the bony fish scale and the concept of soft and hard composite protection. The upper layer of this protective gear is a scale-like layer which consists of periodically overlapping composite scales, the lower layer consists of multiple layers of ultra-high molecular weight polyethylene (UHMWPE) sheets as the backing layer. In accordance with the Level III requirements of the standard GJB 4300A—2012, the protection performance of the protective gear has been tested and simulated with finite element models, and the results verified the good protection performance of the gear against the armor-piercing incendiary bullet, and also confirmed the reliability of the numerical simulations. The results indicate that the thickness of the ceramic layer of the composite scale is one of the key factors that affect the anti-penetration performance of the protective gear. When the total thickness is unchanged, the layer thickness ratio of the composite scale is 2∶1 to meet the protection requirements. Some key mechanisms take effect to determine the anti-penetration performance of the protective gear, including the blunting and lateral deflection of bullets by composite scales, the overall synergistic energy dissipation of the overlapping scales, and the energy dispersion of the UHMWPE backing layer.