The invention discloses a door opening and closing structure applied to a smoke exhaust ventilator. The door opening and closing structure comprises a smoke exhaust ventilator main body and a door plate, and the door plate is movably arranged on the smoke exhaust ventilator main body and capable of rotating relative to the smoke exhaust ventilator main body; and a positioning mechanism which is capable of making the door plate be positioned at any position in rotation is arranged between the smoke exhaust ventilator main body and the door plate. In this way, the door plate can be stopped at any position by a user in rotation through the positioning mechanism, the user can adjust the door plate to rotate by a certain angle relative to the smoke exhaust ventilator main body casually according to requirements, and then the opening degree of a wind suction port of the smoke exhaust ventilator is adjusted, so that different needs of the user are met.