Research conclusions: The comparison is made between the whole load bearing situations of the grid structure of the west and east sub － station building when using a bidirectional spring support and a fixed hinge support． The calculation and analysis show using a bidirectional spring support can much cut the horizontal thrust of the roof grid structure on the column of the bearing frame and the temperature stress． In this paper，the time － history analysis is also made under condition of the seldom earthquake to know the maximum deformation volume of the grid structure support under the effect of the seldom earthquake． The allowable deformation volume of the bidirectional spring support should meet its maximum deformation volume caused by the effect of the seldom earthquake．