On the basis of signal re-organization, a novel method named virtual-position reading method is proposed in this paper. By means of this method, form error or error motion can be respectively separated according to practical needs, and the separating sequence of form error or error motion can also be optional. Furthermore, in the proposed method, it is not necessary to change the conventional measuring and separating system of form error or the normal procedures of separating operation. It is proved that the new method is flexible and convenient in use.