Abstract. It is difficult to seek an optimization design for the falling object protective structure (FOPS) of wheel loader cab. Focusing on this problem, we discuss the topology optimization with SIMP theory under impact condition and the designing parameters, response function and constrain conditions are confirmed. The proposed method is applied to wheel loader cab to get a topology structure. The numerical analysis indicate that the optimized design of wheel loader cab has light weight and can provide sufficient protect for the operator.