An adjustable non-contact seal device used for the main bearing of a large-scale mill is composed of a labyrinth seal plate (2), a seal adjustment platen (3), a three-tongue rubber seal ring (5), a seal baffle (6), an adjustment screw (7), a checknut (8), a grease supply pipe (10), a grease filling connector (11), wherein the step type labyrinth seal plate is welded on a circumference of a main bearing enclosure housing (1), the three-tongue rubber seal ring bonded into a circle is arranged in a step cavity, the step baffle is fixed on the labyrinth seal plate for limiting the position of the three-tongue rubber seal ring in the step cavity; the three tongue component is not contact with a hollow shaft diameter (9) of the mill, the seal adjustment platen is arranged thereabove, the gaps between the three tongues and the hollow shaft diameter are adjusted through a plurality of adjustment screws, and fastened for positioning through the checknut; grease filling gap are formed between three tongues, and the grease can be supplied through a plurality of grease supply pipes and the grease filling connector arranged on the labyrinth seal plate.