Abstract: To explore the anti-penetration abilities of the irregular structure made with high-strength alloy steel, a target enhanced with Ultra-high strength spherical structures (UHS-SS) was manufactured in this work. The UHS-SS is fabricated from ultra-high-strength steel (UHSS) and mechanically anchored to the target via threaded high-tensile rods, ensuring structural integrity under projectile penetration loading. A series of penetration tests under impact velocity of 400m/s were performed using 125mm-diameter artillery. The yaw-induced projectile deflection was recorded at 5000 fps, and thus the failure mode and penetration depth of the projectile were achieved. Though a comparative analysis of anti-penetration experimental results between semi-infinite concrete targets and UHS-SS-reinforced targets, the influences of ultra-high mechanical performances and the spherical yaw-inducing structure on the deflection and fragmentation of the projectile were disclosed. The test results reveal that at a penetration velocity of 400 m/s, the dimensionless penetration depth of UHS-SS target is 0.11, and the penetration resistance of the UHS-SS target is about 9 times that of C40 concrete. The anti-penetration performance of UHS-SS is significantly enhanced in comparison to that of the ordinary concrete target. Furthermore, as the projectile penetrates the UHS-SS target, the resultant force on the projectile is in a different direction from that of projectile velocity, which can deflect and shatter the projectile. The behavior of ricocheting off surface, deflection-induced secondary impact and fragmentation of the projectile occurred during the anti-penetration test of UHS-SS target, and the maximal deflection angle was 83º during the experiment, preventing the projectile form penetration into the interior of protective structure. And the UHS-SS target has a severe erosion effect on projectiles at a lower speed of 400m/s that caused the mass loss rate of projectiles to be 23.66% in the experiment. Therefore, the risk of a ground-penetrating weapon penetrating into the protective works and detonating is significantly reduced．