The invention relates to a sliding rail automatically retracting device. The sliding rail automatically retracting device can solve the problem that existing automatic retracting devices has no sufficient stroke tail end closing force and fails to meet high sealing requirements. The sliding rail automatically retracting device comprises a guide seat, a slider, a limiting unit and a stirring block, wherein the sliding rail is composed of a fixed outer rail, a sliding inner rail and a middle guide rail; a retracting member is hinged to a fixing seat, the fixing seat is provided with a mounting groove, a torsion spring is arranged inside the mounting groove for connecting the fixing seat and the retracting member, and the mounting groove is provided with a torsion spring upper limiting unit and a torsion spring lower limiting unit; the rear end of the stirring block is provided with a traction groove, and the rear end of the traction groove is provided with a guide unit; corresponding to the traction groove, the retracting member is provided with a retracting column and a stirring column; when the fixed outer rail and the sliding inner rail are closed, the stirring column of the retracting member is clamped inside the traction groove of the stirring block, the guide unit is positioned between the retracting column and the stirring column, and the torsion spring is limited by the torsion spring upper limiting unit.