It is a protective device of alarming and stopping to prevent the rotator of steam turbine from exceeding the axial displacement in the axial displacement. The gap between the oil-spray nozzle and oil baffle disc is 0.5mm( at this moment the gap between the thrust disc and main thrust tile is Zero), when the relative displacement of rotator is 1mm( namely the gap between the oil-spray nozzle and oil baffle disc is increased by 1.5mm), the spring force on the slide valve is larger than the control oil pressure, the slide valve is sliding to turn off the high-pressure oil to the main steam valve manipulating pedestal and extraction check valve, so that the extraction check valve of the main steam valve is quickly closed, in the mean time the high –pressure oil enters the lower part of the staggered oil valve to make the control valve close quickly. This device can be stopped manually, it can be stopped by the silver handle knob of manual-device. If the unit is required to start, after the high-pressure oil is supplied, manually push the handle knob to make the sliding valve end seal with the seal surface of the extension arm end.