The members and joints are the two major components of a single-layer gridshell, and are also important factors that significantly affect the stability performance of the structure. With the development of the construction industrialization in China, scholars have developed many semi-rigid new types of joints. Compared with traditional joints, these new joints are neither ideal rigidly connected nor ideal hinged. However, in the current design method of single-layer gridshells, it is still assumed that the joints are ideal rigidly connected first, and the member design is carried out. Then, the stability calculation is based on the assumption of rigid joints. This two-stage design method not only disconnects the mutual influence between members and joints, but also restricts the use and promotion of new types of joints. Related research results have shown that the stiffness of the joints has a significant impact on the stability performance of the gridshell. Therefore, there is still room for improvement in the current design method. This chapter further expands the theory of shape fragility, introduces joint stiffness into the theory of shape fragility, defines the relative change gradient of shape degree of freedom gra_r for semi-rigid joints, and reveals the instability mechanism of single-layer shell structures from both the beam and joint levels. Then, taking a single-layer shell structure as an example, the chapter quantitatively examines the influence of joint stiffness on the stability performance of the shell structure from the perspectives of structural stable bearing capacity and joint shape degree of freedom. It determines the reasonable range of joint stiffness suitable for design. To consider the influence of both the joint and the beam on the stability of the shell structure at the same time, this chapter proposes a stable optimization design method for single-layer shell structures considering joint stiffness. The optimization model takes both the beam and the joint as optimization variables, maximizes the minimum value of the relative change gradient of joint shape degree of freedom gra_rmin as the optimization goal, considers the constraints of steel usage for beams, joints, beam design limits, etc., and develops corresponding optimization algorithms. Three single-layer shell structures with different spans are used as examples to verify the stable optimization design method considering joint stiffness. The stable optimization results of three examples show that the stable optimization design method considering joint stiffness can optimize the distribution of beam section and joint stiffness under the premise that the steel used at joints is significantly lower than that of the traditional design method, thereby improving the stability bearing capacity of single-layer shell structure. Furthermore, the method verifies the anti-collapse performance of semi-rigid joint optimized shell structure, and the calculation results show that the maximum displacement response of semi-rigid joint optimized shell structure in a 9° rare earthquake is basically the same as that of the rigid joint optimized shell structure, and its collapse critical seismic acceleration peak value is significantly higher than the peak value of the 9° rare earthquake seismic acceleration specified in the seismic code.