Provided is a closed sputum suction tube. The closed sputum suction tube comprises a T-shaped three-way valve, a liquid injection tube device is arranged at the inserting end, connected with the T-shaped three-way valve, of the sputum suction tube, and an electromagnetic valve is arranged in the connection portion of the liquid injection tube device and the inserting end of the sputum suction tube; the electromagnetic valve is connected with a controller, an annular flowmeter is arranged on the head of a conical end of the inserting end of the sputum suction tube, and the annular flowmeter isin an annular shape with thickness; four through holes are formed between an inner circle and an external circle in the radial direction, a pressure sensor is arranged between every any two adjacent through holes, and signal wires of the pressure sensors in the annular flowmeter are connected with the controller; an anti-suction-back device is embedded in a joint of a sputum suction tube body which is connected with the T-shaped three-way valve 1. The closed sputum suction tube can monitor sputum flow in the sputum suction process and control opening and closing of the electromagnetic valve, added medicine liquid or washing liquid dilutes sputum which is difficult to suck, and the closed sputum suction tube has the advantages that the closed sputum suction tube is automatic, saves time andimproves the safety of sputum suction.