Abstract: In this paper， the vibration attenuating function of L-shaped plates with blocking mass is analyzed based on the wave theory， and such attenuation techniques are introduced in the vibration isolating design of cabin shells by incorporating the principle of impedance mismatching and wave conversion. Particularly， the vibration characteristics and sound radiation properties of the shell （with and without the blocking mass） are calculated numerically. Furthermore， the influence of the mass's weight as well as its sectional dimension on the vibration isolating performance is discussed， and an optimization design is proposed accordingly. The results show that the presented L-shaped plate not only reduces the vibration of engine cabins， but also significantly suppresses the vibration transmission to the adjacent cabins. Meanwhile， it is observed that as long as the total weight of the isolation mass remains constant， arranging the blocking mass properly with variable weight and cross-sections could enhance the performance of vibration isolation and noise reduction.