A screw with a flat drilling end comprises a cylinder (1) with a thread (11) wrapped around and a flat drill portion (2) longitudinally extended from a distal end of the cylinder (1); a maximum thickness (T) of a transversal cross section of the flat drill portion (2) being less than a half of the maximum width (D) of the transversal cross section of the flat drill portion (2); the maximum width (D) of the transversal cross section of the flat drill portion (2) being smaller than an outer diameter of the thread (11) of the cylinder (1); the width and thickness of the transversal cross section of the flat dill portion (2) being reduced to a point tip end of the flat drill portion (2). Two opposite lateral sides form as sharp knife blades.