This study establishes the scheme on the noise reduction of the interior cavity of a passenger car using the mode coupling coefficient between the structural vibration modes and the acoustic modes. A dominant noise level is identified on the running test. To reduce its level, the mode coupling analysis is carried out using pre-determined acoustic modes and structural modes. The structural modes is obtaind from modal testing for the passenger car. The acoustic modes of the interior cavity is calculated by finite element analysis. The noise level is reduced efficiently by a structural modification of the boundary panels which strongly contribute to the Interior noise. These procedures are carried out by using an user friendly computer program (ACSTAP) which is developed in this study.