In order to elucidate the action of the STM tip in the manipulation of atom on a sample surface, the interaction between W tip atom and sample Al(111) surface atom is studied with cluster model by employing the first principles method—discrete variational method. The calculated results show that if the distance S between the tip and sample surface is short enough (S≤10 a.u.), when the sample surface Al atom, which is just under the W trp, escapes from the surface, it fells a stable potential well. This indicates that even without an external field, the Al atom can be extracted from the sample surface to the tip ty the attraction of the W tip, if the tip is very close to the sample surface.