The invention discloses a laminar flow cover mechanism having a cover plate. The mechanism comprises a cover, wherein an air inlet is molded in the cover; a vertical rectangular ventilation pipe is fixed in the air inlet; a cover plate mounting notch is molded in the upper end surface of the opening lower end of the rectangular ventilation pipe; the inner wall of the cover plate mounting notch is hinged with a rotating shaft; the rotating shaft is fixedly coated with an inclined cover plate; the two ends of the rotating shaft are fixedly inserted with two driving bevel gears; one sides of the driving bevel gears are engaged with driven bevel gears; transmission rods are fixedly inserted in the driven bevel gears; one ends of the transmission rods are fixedly inserted with locking blocks; two guide rail strips are molded on the two side surfaces of the cover plate; brush mounting bases are pressed against the guide rail strips; the lower ends of the brush mounting bases are fixedly connected with connecting rods; the upper end surfaces of the brush mounting bases are fixedly connected with strip-shaped brushes; and the locking blocks are pressed against the brush mounting bases at one sides of the strip-shaped brushes. The mechanism can realize automatic closing of the air inlet when a laminar flow cover dose not work, and can remove stacked dust and impurities.