Sensitivity analysis is to evaluate how sensitive the surface deviation of a workpiece is to a geometric error of locator. With this thinking, the relationship between geometric error of locators and the position error of holes group is presented. The fixture system errors model and evaluation model of position errors are established. Furthermore with both models, a method of optimizing the position errors by adjusting the locators’ position is presented, which can get to accuracy localization. At last, a simulation study is used to verify the method.