Automatic opening/closing device for flue

The invention provides an automatic flue on/off device which can realize on/off switching of a flue through remote automatic control under the condition that a parallel unit is not shut down. The device comprises a flange jacking/locking mechanism, a composite plugging plate, a composite plugging plate coiling mechanism and a traction mechanism, the assembly type lower flange assembly is connected with the compensator through the assembly type upper flange assembly, and the flange jacking/locking mechanism is used for jacking the assembly type upper flange assembly so that an opening space can be formed between the flange jacking/locking mechanism and the assembly type lower flange assembly. Or the flange of the compensator assembly is pulled down, so that the flange is locked with the assembled lower flange assembly or the plugging plate; the composite plugging plate coiling mechanism is used for releasing or recovering the plugging plate; when the plugging plate curling mechanism releases the plugging plate