Fire in the large volumn spacial buildings is defined as localized fire.The structural integrity can cause restriant effect in the members of grid structure subjected to localized fire.The slenderness ratio of members in actual grid structure is often greater than that of the steel frame structure column.There is no research on the post-buckling loading-bearing capacity of restrained members in grid structure.A simple method for calculating the post-buckling load-bearing capacity has been derived from the force equilibriums of restrained steel members in fire condition and is verified by the ABAQUS software.The axial force-temperature relationship of a restrained steel member can be obtained.It is also found that the initial crookedness can slow down the growth rate of stress

especially for the members with high value of slenderness ratio.The post-buckling load-bearing capacity of members can improve the fire-resistance capacity of the steel grid structure.