The invention relates to a vacuum system exhaust noise reduction method, a noise reduction device and a vacuum system. The noise reduction device comprises a first baffle valve, a bypass pipeline, a second baffle valve, a vacuumizing valve relay and a power-off delay type time relay, wherein the first baffle valve is arranged on a vacuum pipeline, and the inner diameter of the first baffle valve is the same as the inner diameter of the vacuum pipeline; one end of the bypass pipeline communicates with the vacuum pipeline on one side of the first baffle valve, the other end of the bypass pipeline communicates with the vacuum pipeline on the other side of the first baffle valve, and the inner diameter of the bypass pipeline is 0.1-0.2 of the inner diameter of the vacuum pipeline; the second baffle valve is installed on the bypass pipeline, and the inner diameter of the second baffle valve is the same as the inner diameter of the bypass pipeline; and the vacuumizing valve relay and the power-off delay type time relay are connected in series, the vacuumizing valve relay is connected with a PLC, a normally closed contact of the time relay is connected with a control line of the first baffle valve, and a normally open contact of the time relay is connected with a control line of the second baffle valve. According to the vacuum system exhaust noise reduction method, the caliber of an air suction pipeline is switched to reduce the air vibration, so that the sharp noise generated at the moment of vacuumizing can be effectively reduced.