A three-sectional hidden sliding rail includes a pair of sliding rail sub-mechanisms symmetrically mounted at a left and a right side of a movable object. Each sliding rail sub-mechanism includes a fixed guide rail, a middle rail, and a movable guide rail. The fixed guide rail is mounted on a fixed object. The movable guide rail is mounted on a side surface of the movable object. The fixed guide rail and the movable guide rail (3) have a sliding guide groove. An upper and a lower end of the middle rail are mounted in the sliding guide grooves of the movable guide rail and the fixed guide rail. The middle rail is able to slide along the sliding guide groove of the fixed guide rail (1), and the movable guide rail is able to slide along the middle rail (2). The sliding rail sub-mechanisms are connected through a synchronous mechanism.