A cutting machine for cutting window coverings includes a machine base, on which a cutting device and a clamping device are mounted. The cutting device has a cutter. A blade edge of the cutter is oblique to a sustaining face, on which the window covering is rested, of the machine base. It is beneficial to cut a first rail, a covering material, and a second rail of the window covering in sequence. The cutting machine may cut the window covering with a flat cutting facet to have a good cutting quality and also extend the life of the cutter.