Abstract: In robust optimization mechanical design, uncertainty variables are often assumed to be stochastic variables complying with special distribution and these uncertainty variables' original data are discarded, in the succedent optimization design model. That method cannot often reflect these uncertain variables' essence, consequently a far-from-fact conclusion is obtained. In order to describe these uncertain variables actually, the uncertain variables in mechanical design were expressed in blind number and the relation between variables was expressed in the operation rule of blind number. Combining the blind number theory and the robust design method, a robust optimization design model was built. Using this model in optimization design of an air driving reversing device, the result is better than that from traditional robust design. The method based on blind number is a kind of discrete numerical calculation method, and the example unfurls its flexible fully and proves that this optimization method is reasonable and practicable.