Abstract: Considering internal heat conduction, the thermal bending deformation of grid sandwich beam when one side was heated was studied. It is assumed that the webs in the middle layer of the sandwich beam did not bend when the beam deformed. Taking the periodic character of the grid beam structure into account, the relationship of the internal force and the displacement was got through the equilibrium equation and the deformation coordination of the cell. By transfer matrix, the expressions of internal force and deformation of the sandwich beam depending on temperature were stablished. Using present model, the deformation of cantilever grid sandwich beam whose upper surface was heated was calculated. For the case that the number of cell is larger, the height of webs is smaller and the thickness of webs is close to one of panels,the deflection results computed by the presented model are in good agreement with finite element results.