Research conclusions: (1) If the cast － steel joint is used for the long － span steel canopy，it can avoid the residual stress when welding multiple bars and its shape can meet the requirements of architectural modeling because of the big freedom．(2) The failures in strength and stability and deformation of joints can be known and compared with the design code by using finite element method．(3) The stress can be cut，the joint stiffness can be enhanced and the partly deformation of the joint can be avoided by reasonably setting the wall thickness of the joint and the internal reinforced rib to meet the the design requirements．(4) The conclusions can be used in joint design of long － span steel structures，such as grid，truss and so on．