The deflection of focused beam propagation direction when the metal plate is cutting by numerical-control (NC) laser cutting machine is studied. Several incidence physical parameters affecting the direction of focused beam when the energy center lines of the laser beam and the optical axis of the convex lens are in different planes are found out. The relationship between them is given by geometrical optics. It is found that we can change the direction of focused beam by shifting the convex lens. The testing results show that the horizontal movement of the convex lens can change the direction of focused beam. This method is also applicable to other laser processing equipments which use convex lens. It provides a new selection on the direction-adjusting design of focused beam.