The invention discloses a trimming device for garden trees. The trimming device comprises a fixed rod, one end of the fixed rod is provided with a telescopic rod, the end, away from the fixed rod, ofthe telescopic rod is provided with a trimming device body, one side of the telescopic rod is provided with a supporting frame, one end of the supporting frame is connected with the telescopic rod through a movable sleeve, and the end, away from the telescopic rod, of the supporting frame is provided with a clamping device; the trimming device body comprises a fixed plate, the lower end of the fixed plate is connected with the telescopic rod, one side of the fixed plate is provided with a first fixed block, a first movable rod is inserted in the first fixed block, the upper end of the first movable rod is provided with a first movable block, the end, away from the first movable rod, of the first movable block is provided with a second movable rod, one side of the first movable block is provided with a first rack, the upper end of the second movable rod is provided with a first blade, the side, located on the fixed plate, on the second movable rod is provided with a second fixed block,and the side, located on the fixed plate, of the first fixed block is provided with a third fixed block.