Abstract: An uncertain optimization method is suggested to solve the uncertain engine crankshaft problems based on the nonlinear interval number programming and the interval analysis method. The uncertain parameters are treated as the intervals. The maximum value of von Mises stress is considered as the objective function and simulated by the finite element method. The nonlinear interval number programming is used to dispose the uncertain objective function. The interval analysis method is applied to calculate the interval of the objective function efficiently. The intergeneration projection genetic algorithm is employed to seek for the optimum of the uncertain problem. The results of the example demonstrate the efficiency of the presented method.