The principle of stiffness offset with the positive and negative stiffness parallel were introduced and through analysis the natural frequency and the vibration transmissibility can be reduced.

By means of the analysis on parallel vibration isolation mechanism of positive and negative stiffness, a new typed parallel nonlinear ultra-low frequency horizontal vibration isolation system with positive and inverse pendulums was developed.

A novel combined positive and negative stiffness isolator was developed based on the analysis of the mechanism of negative stiffness in this paper, whose negative stiffness cancels much of the positive stiffness of the elastic element in the vicinity of balance point.

The methods of realization of nonlinear stiffness and applications of combined positive and negative stiffness in ultra-low frequency vibration isolation are analyzed.