A multidisciplinary optimization method about the thickness of engine hood based on pedestrian protection was proposed. The impacting zones of engine hood where HIC values of original engine hood were higher than the safety value of 1000 were selected as the cases of optimization. At the same time, the stiffness of torsion of engine hood and the deformation distance between the hood and the underneath hard parts in the engine bay were taken into account. The objective was the minimization of hood deformation above where the hard parts were located. The first type of constraint was that the HIC values were less than the safety value 1000 in the selected cases of optimization. The second type of constraint was that the torsion stiffness of engine hood was higher than that of the regulation. The pedestrian protection optimization model about the thickness of engine hood was constructed and solved. The results of optimization indicated that the obtained thickness by this method improved the performance of pedestrian protection.