Abstract: The relations between force transmission coefficient of the system to its foundation，the characteristic amplitude of the working mass and the system dynamics parameters were deduced by theoretically analyzing a vibrating system with dual masses. Coefficient of vibrating material， critical frequency ratio and its difference， and the increase in characteristic amplitude were defined. Through numeric analysis， the domain where the force transmission coefficient was less than 10% was determined. The conclusions show that with isolation frequency ratio increasing， force transmission coefficient reduces and characteristic amplitude increases. And characteristic amplitude does not increase with adding of vibrating material mass when the mass ratio is more than 0.57. The less mass ratio of the working body is， the larger the possibility of domain with the low force transmission coefficient and large characteristic amplitude is realized. The method to determine the system dynamics parameters is proposed to ensure the vibration isolation effect， the vibrating material of maximum coefficient， the characteristic amplitude and the increase in characteristic amplitude.

Key words: dual-mass, vibration isolation, force transmission coefficient, characteristic amplitude, vibrating material