As a new type of prefabricated joint, the bulge formed joint has advantages such as good load-bearing shape, low stress concentration coefficient, and fatigue resistance. The bulge plate of the new proposed joint is a free form surface structure, and the forward design problem of this structure is the key limiting factor for its application. In this paper, the Non-uniform rational B-spline (NURBS) modeling method is used to establish the bulge plate surface model, firstly. Then, the curvature variation law of the surface is analyzed through control points of NURBS surface, and the curvature distribution of the surface is used to characterize the fairness characteristics of the surface. And the model of different surfaces are created using the orthogonal design method, and the mechanical properties of each surface, such as ultimate bearing capacity, strain energy density and maximum stress, are analyzed through numerical method, in order to study the influence of fairness characteristics of the bulge plate surface on the mechanical properties of joints. On this basis, a response surface model is established, and genetic algorithm is used for multi-objective optimization. The optimization results show that under the premise of little change in mechanical properties, the fairness characteristics have been greatly improved.