The target cascading and the surrogate model are employed for the design optimization of underwater structural vibration and acoustic radiation. The target cascading is used for multilevel optimal design and the surrogate model based on computationally efficient Kriging approximations is applied for predicting vibro-acoustic response. A design optimization problem of a two-level modeling hierarchy of a stiffened plate underwater is formalized to show the optimization procedure. The design variables are the plate thickness and the stiffener dimensions. The objectives of the optimization include the minimization of the structural mass, the maximization of the fundamental resonant frequency and the minimization of the corresponding radiated power level, and the maximization of the difference between two chosen resonant frequencies. The results show that the surrogate model gives very good approximation of the coupled computation model for predicting the resonant frequency and corresponding sound power level with no computation time delay. The target cascading can be properly used for design optimization with different design tasks and different coordination strategies.