Research conclusions: ：(1)The elastic support of the diaphragm affects the whole load—bearing capacity of the section of box beam to some extent and the transverse beam can easily and directly improve the load——bearing capacity of the roof，SO with consideration of the advantages of each design program，an integrated program should be made to improve the load—bearing capacity of box beam．(2)It can be seen from the change law of axial force of boom that the axial force of the boom in all calculation programs has no change basically．It shows the diaphragm or transverse beam installation only changes the transverse rigidity of box beam and has a little influence on the vertical rigidity of box beam， and it also verifies again the elastic support effect of the diaphragm only changes the force transfer way in the box beam and has no obvious innuence on the rigid ratio of the beam and arch．