Abstract: To investigate the influence of polyurea back coating thickness on the impact resistance of automotive steel panels, low-speed drop hammer impact tests with an impact energy of 100 J were conducted for four different polyurea-plate composite structures with different coating thicknesses and steel panel. LS-DYNA simulation software was utilized to numerically simulate the test conditions, and the simulation results were within the acceptable engineering error range. The experimental results were consistent with the simulation results. Furthermore, a comparison was made between the impact resistance of the composite structures and pure steel panels with the same areal density. Based on these findings, the impact of coating thickness on the impact resistance of the back-coated structures was further investigated. The results reveal that the back-coated structures exhibit superior impact resistance compared to the structures without spray coating. Under the condition of equal steel plate thickness, increasing the coating thickness effectively improves the structural stiffness, but the degree of improvement decreases as the ratio of polyurea to steel plate thickness increases. Under the condition of equal areal density, the coated structures demonstrate better potential for impact resistance compared to the pure steel panel structure. Under the condition of equal thickness of steel plate, the specific energy absorption of polyurea-plate structure increases first and then decreases with the increase of the thickness ratio of polyurea to plate, and it exists an optimal thickness ratio.