Abstract: Focused on 3-dimensional seismic isolation for latticed roofs,the mechanism and device in vertical direction of the bearing are discussed.Firstly,absolute isolation effectiveness (S_ie) is introduced.Based on S_ie,the relationship between vertical stiffness and characteristic frequency of input excitations is established, and it verifies that means of seismic isolation in vertical direction is realizable.Then the formula for stiffness in vertical direction is developed.Finally,some parameters related to the design of springs are analyzed,and the practical measures are established as well.