Disclosed is a method for operating a liquid slag flow control device having the functions of rapid replacement and handling accidents. When a straight pipe segment (37) of a slag drop pipe needs to be replaced during operation, a stopper rod head (18) is tightly stoppered by means of a stopper rod push device (17), and an accident flow guide groove (16) is also pushed above the straight pipe segment (37) of the slag drop pipe by means of an accident flow guide groove push device (15), thus preventing molten slag from entering the straight pipe segment (37) of the slag drop pipe via a metering port (19).