The closed air hood is a house-like device, which is installed in the dryer section of the paper machine. It is composed of steel structure and thermal insulation layer. The hood body is provided with a roll changing door that facilitates the maintenance of the paper machine roll changing, a movable door for personnel to enter and exit, and a lifting door that facilitates employees to operate the paper machine. Lighting and fire fighting systems are installed in the hood. Blowing boxes and air duct systems in the hood are also provided to improve the convection of moisture in the middle of the dryer. The closed air hood covers the drying staff of the paper machine in a closed environment, so that the moisture and hot gas in the paper sheet evaporated by the drying cylinder are concentrated in the hood without diffusing into the workshop environment, and are collected centrally and discharged through the suction effect of the external exhaust system.