Abstract In the double-stage vibration-isolation system the relationship of three evaluation indices of vibration-isolation (vibration level difference, insert loss and force transmissibility) is researched. By theoretical analysis a conclusion is got that these three evaluation indices have a constant difference under certain conditions. A passive vibration-isolation experiment is designed, which results indicate that these three evaluation indices have the same trend and their differences maintain constant values. The experimental results verify the previous conclusion. Moreover the simulations are caught out after changing the system damping and stiffness respectively. Through the comparison of the simulation results and experimental results of these three evaluation indices, the relationship between these indices and the system damping, stiffness and mass is analyzed.