With an application of fuzzy finite element theory, in conjunction with an improved cut-level set method that considers different properties of constraints, a fuzzy finite element optimum mathematics model whose objective function is mass of the three-axis table frame is built. So the fuzzy optimum problem is transformed into the ordinary optimum problem using Sequential Unconstrained Minimization Technique (SUMT) to solve. A general optimum method is developed for the design of three-axis simulating table structure. An application is given. The results show that the mass of frame decreases by 8.7% compared with the ordinary design with the deterministic boundary constraints. The practical application of example is feasible in the project, so the method could be applied efficiently to practical engineering problems.