Abstract: Carbon Fiber (CF) composites are widely used in the field of aerospace protection due to their high strength and low density. To investigate the effect of carbon fiber (CF) backplate thickness on the impact resistance of Al plates, the experiments using a musket were conducted to launch an 8 mm tungsten alloy spherical projectile at Al/CF composite plates. The dynamic response and internal damage of the composite plates under different impact conditions were examined by digital image correlation (DIC) and computed tomography (CT). The effect of CF plate thickness (0.7~12.6 mm) on the energy absorption performance of Al/CF composite plate was studied based on the finite element model of fragment penetration of Al/CF composite plate. The results show that the aluminum plate is subjected to shear failure under the impact, the inner fiber is damaged with compressive shear, while the outer fiber is deformed by tensile deformation. The failure crack extends along the fiber direction and the delamination is significant. The energy absorption of Al plate does not increase significantly under the penetration of projectiles (1000 m/s, 1250 m/s, 1500 m/s) when the CF plate increases to a certain thickness (4.2 mm, 5.6 mm, 5.6 mm), and the impact kinetic energy of Al plate is 1008.02 J, 2061.84 J and 2868.61 J, respectively. The fiber layer position affects the change of the fiber damage area and the fiber damage shape, the fiber damage area decreases firstly and then increases along the direction of fiber thickness, and the fiber damage shape changes from oval to elongated along the direction of thickness. With the fiber thickness increase, the specific energy absorption of Al/CF composite plate decreases linearly with the areal density increase.