A swinging mechanism for a lawn sprinkler includes a sprinkling control unit with a gear-operated transmission mechanism adapted therein attached to one side of a sprinkler mount thereof. A limiting connector having a water outlet connector engaged at one side is correspondingly matched to the gear-operated transmission mechanism and a sprinkler body. A main driving wheel, an adjusting seat, and a water inlet connector are sequentially coupled at the other end of the gear-operated transmission mechanism thereof. A flow switch plate, a switch device and a retaining pole are mounted to a limiting groove of the adjusting seat thereof. The switch device, of a frame body, has resilient ribs extending centripetally at the inner side meshing with an adjusting serrated section of the retaining pole, inverted U-shaped resilient sections with stop blocks abutting against one side of protruded guide blocks of the limiting groove thereof, and indented control sections to retain both ends of the flow switch plate therein. To swing back the sprinkler body at the limiting end, the switch device is rotated at the limiting groove of the adjusting groove therein via the retaining pole coupled with the gear-operated transmission mechanism at one end, instantaneously pushing the stop blocks over to the other side of the protruded guide blocks and activating the flow switch plate to move therewith so as to precisely switch the angle of water discharge and effect the operation of the sprinkling control unit in an easy and smooth manner.