The interval finite element model is used to design an uncertain structure. Using interval extension, the interval element stiffness matrix of the structure is recorded as median matrix plus increment one of the element. They are assembled as an interval global stiffness matrix. Then the interval displacement vectors can be derived from the structural equation to obtain the interval constraints. Improved grey wolf optimization algorithm is applied to the interval finite element structure for optimal design. The strategy is adopted to determine the individual position, which makes the convergence factor show nonlinear fluctuation, thus speeding up convergence of the program. The optimal result of an interval space finite element truss proves the feasibility of the method.