Abstract: Active sound insulation system of elastic plates excited by a reverberant sound field is optimized in this study. According to the excitation frequency range,the modes to be controlled are determined and a reduced-order equation is established in the modal space.Based on pole assignment method,a distributed system is employed to increase the modal damping of the controlled modes so as to suppress the low- frequency resonance transmission under the reverberant field excitation.The state information required by the controller is estimated by a modal filter.To enhance the control performance,optimal placement of the sensors and actuators is investigated,different control schemes are examined,and the sound transmission losses under coupling control and independent modal space control(IMSC) are compared.It is shown that,active sound insulation system based on pole assignment method in this paper can suppress the resonance transmission,and less control force are required by IMSC system with optimal placement of the sensors and actuators. It is concluded that control performance of the optimal active sound insulation system is enhanced.