An inflatable membrane structure derives its structural integrity from pressure difference, so as to support its self-weight and other external loads. To increase the bearing capacity of membranes, cables with more strength are added to adjust the shape and stress distribution. Form finding is critical for inflatable cable-membrane structures, and pressure difference is the key factor that influences the shape and stiffness of the inflatable structure. Based on the nonlinear finite element theory, the concept of pressure difference presetting was proposed and combined with the nodal equilibrium method for optimization. According to the design goals of airships, the form finding scheme was put forward to achieve multi-objective optimization. First, the geometric shape that satisfies the specific stress ratio between the cable and the membrane was obtained by combining the pressure difference presetting method and the nodal equilibrium method. Then, the final shape with expected volume was achieved by scaling up and down. Results show that the stress of the cable after form finding was twice as large as that before form finding, where the cable fully exerted its load-bearing effect. In addition, the stress distribution of the membrane was more uniform, and the bearing capacity of the overall structure was strengthened. The study can provide reference for solving practical engineering problems.