Abstract: A dynamic optimization method based on admittance method and genetic algorithm was presented to optimize grillage structures considering their sound radiation characteristics.In the analysis,the grillage system was first separated into a plate and some discrete beams and then the admittance method was employed to calculate the dynamic response of the grillage system with vibration isolators,which was more efficient than one using the finite element method.And together with the boundary element method,the acoustic radiation power could be computed easily.The inertia moments of the beams were selected to be design variables in the study to reduce the number of optimal variables and the computational burden was greatly reduced accordingly.In order to obtain discrete optimal results a scheme database was constructed and from which the possible design scheme was selected based on the inertia moments of the beams that were determined by genetic algorithm.A numerical example showes that the dynamic response from the admittance method is well agreed with one obtained from the finite element method.A dynamic optimization example is also provided to demonstrate the validity and effectiveness of the proposed optimal method.