Abstract: In order to analyze the vibration characteristics of mechanical systems from vibration transitivity， a model of vibration transfer path system composed of excitation sources， transfer paths and recipients was established. Among the subsystems， transitivity of transfer paths determined the response characteristics of recipients and became an important part in vibration and noise reduction system. A concept of path insertion loss was proposed and the convenient and effective formula was derived using the path separation method. So the path contributions can be evaluated based on the corresponding results in frequency domain. In a numerical example， the results were satisfying， which further indicated the effectiveness of path insertion loss as an evaluation of path contribution.

Key words: mechanical system, vibration characteristics, transfer path, path contribution, insertion loss