In order to study the mechanical response characteristics of debris flow deposits under the impact load of high-speed projectiles, the time-history curves of acceleration, velocity, displacement and stress of projectiles penetrating debris flow deposits were analyzed by means of impact load model experiment and numerical simulation. The characteristics of motion attitude, resistance and cavity in the process of projectile penetration were analyzed. The experimental results show that when the projectile penetrates the debris flow deposit, the displacement increases rapidly. With the instability of the motion attitude of the projectile in the debris flow deposit, the deceleration gradually increases. When the axial direction of the projectile is perpendicular to its motion direction, the contact surface is the largest, the resistance reaches the maximum, and the negative acceleration also reaches the maximum. During the penetration process of the projectile, the projectile arranges the debris flow deposit around to form a large cavity, and the velocity of the projectile decreases and the displacement increases slowly. During the penetration process of the projectile, with the increase of time, the projectile flips over, and finally the tail begins to move forward. The contact surface between the debris flow accumulation body and the debris flow accumulation body decreases, the resistance decreases, the acceleration decreases, the speed is relatively slow, and the curvature of the displacement curve decreases with the decrease of the speed. The research results can provide important reference and theoretical support for the design and safety assessment of high-speed projectiles in the mechanical response characteristics of debris flow deposits.