Impedance gradient provides an effective lever to reduce transmitted peak pressure under impulsive loading. However, discrete multilayer designs are prone to interfacial delamination, whereas continuous hard‑to‑soft gradient designs still promote rear‑face energy localization. Here we introduce a continuous architected gradient featuring a non‑monotonic, valley‑shaped impedance profile that activates an impact energy‑trap and suppresses rear‑face localization without creating material interfaces, thereby enhancing transmitted‑pressure attenuation. The impedance gradient design is realized using a density gradient Gyroid structure. To efficiently predict transmitted peak pressure and elucidate the propagation of nonlinear stress waves, an innovative theoretical model is developed that considers the non-monotonic spatial distribution of material density and the nonlinear elastic response characteristics. Its results shows that the pressure attenuation of impedance‑valley designs outperform conventional design of linear decreasing impedance distribution. Further analysis reveals that this enhanced mitigation stems from the formation and maintenance of impedance valleys by density valleys and material strain softening behavior, which enables energy retention within the structures by forming an impact energy trap. Subsequently, the influence of impedance valley shape on pressure attenuation performance is discussed. Finally, the enhanced impulse mitigation performance of impedance-valley architected materials is validated by conducting shock tube experiments. The peak pressure of impulse loading is decreased by 33% compared to conventional linear negative gradient structures.