The present invention discloses a method and system for machining a work piece by a machining tool, and a robot system using the same. The method comprises: defining a customized contact point on the machining tool by setting a contact point height of the machining tool; moving the machining tool against the work piece to apply predefined machining feeds. Compared with the existing prior arts, the proposed method and system improves machining efficiency and accuracy. With the method and system according to the present disclosure, high machining efficiency could be achieved as well as collisions could be avoided.