The invention provides an ultrasonic flowmeter probe disassembling and assembling method. The method comprises the steps that a card board, two screws and two positioning nuts are prepared; three notches are formed in the wide face of one side of the card board at equal intervals, and the full-threaded screws and the positioning nuts are included. The two screws are welded to high pressure water pipes at the two sides of a probe; the card board notches are clamped on the probe and the screws at the two sides. The positioning nuts are loosened, the card board is taken down, a ball valve arranged on the probe is switched on, and a probe rod is pushed up by means of high pressure water. The ball valve is switched off, a connecting nut is loosened, and the probe is taken down to be cleaned or replaced. The card board is reassembled, and then the ball valve is switched on; the two positioning nuts are tightened, the probe is pushed to the working position through the card board, and the connecting nut and a locking nut are tightened. Accordingly, ultrasonic flowmeter probe disassembling and assembling can be conducted online without cutting off water supply, so that the blast furnace staying accident is avoided, the fault is treated in time, the fault treatment time is shortened, the accident loss is reduced, and smooth production is guaranteed.