A guiding rail system for a car curtain comprises: a guiding rail main body in strip which is separatively set on the interior trim on both sides of a windshield, in combination with a car curtain; it is characterized in that: plural positioning parts in sheet with an U-shaped section, which have a bottom, a front clipping piece and a rear clipping piece for clipping on the destined edge of the interior trim; and plural snap pieces, wherein the first end of the snap pieces is set in the guiding rail main body, while the second end of the snap pieces is easily inserted in or detached from the gap between the front clipping piece and the interior trim, thus a guiding rail main body that is easily assembled and disassembled is achieved.