The invention discloses an aluminum electrolytic tank closed gas collecting device, and relates to the technical field of aluminum electrolytic tanks. The aluminum electrolytic tank closed gas collecting device comprises a mobile cart, an adjusting mechanism, a gas collecting hood plate, a connecting hose and a flue gas processing mechanism. The adjusting mechanism is fixedly arranged on one sideof the position above the mobile cart and includes a rotation component, a lifting component, an extension component and a pressing component, the rotation component is fixedly arranged on the mobilecart, the lifting component is fixedly arranged on the rotation component, the extension component is fixedly arranged on the lifting component, and the pressing component is fixedly arranged on the extension component; a gas collecting hood is fixedly arranged on the extending end of the extension component; and the flue gas processing mechanism is fixedly arranged on the other side of the position above the moving cart, and the gas collecting hood and the flue gas processing mechanism are in communication through the connecting hose. By means of cooperation of all components in the device, flue gas generated in the aluminum electrolytic tanks can be better collected and processed, environmental damage caused by the fact that harmful gas is emitted into the air is prevented, and the practicability is high.