The invention discloses a dot mode ATO protection method under a degradation signal system. Under the degradation signal system, onboard equipment of a train obtains dot mode movement authorizations by receiving interlocking information sent by transponders or beacons of semaphores on tracks, calculates to obtain the states of the semaphores in front, the speed limit information, safe stop stations, non-safe stop stations, target stop stations and the distance to the target stop stations according to the route blockage principle and the train position and automatically drives the train according to the information. According to the dot mode ATO protection method, the train can be automatically driven in a backup mode.