A cutting machine for window coverings is disclosed, which includes a worktable, a first cutting device, and a caliper. An abutting member and at least one series of extending graduation marks are provided on a table surface of the worktable. The caliper includes at least one internal gauge point and at least one external gauge point. By making the internal gauge point or the external gauge point of the caliper point at a scale value of the series of extending graduation marks which matches a height of a window opening, and by cutting the slats, the resultant slats are adapted to be installed to the window opening. In addition, a distance between a surface of the first cutting device which bears the slats and the table surface of the worktable is short, which makes the stacked slats can be cut in a substantially horizontal way.