The invention discloses a dual-computer redundancy fault-tolerant system and the redundancy switching method. The system comprises an A computer, a B computer, redundancy switch control units in the A and B computers transmit respective switch signals to a redundancy switch selecting unit, and the final control signal generated by the redundancy switch selecting unit is transmitted to a controlled unit. The redundancy switch control unit includes an arbitrary switch unit, a heartbeat receiving unit, a power on-off unit and a monitoring unit. The method comprises the following steps: the two computers are powered up, a master computer and a slavery computer are decided by power up strategy; the states of the two computers are judged; if the two computers have no fault, the task segment of a system is judged: if the system is in normal task segment, a working computer powers up a backup computer, and executes cold backup strategy; if the system is in key task segment, the working computer powers down the backup computer, and executes hot backup strategy; if a single computer has fault which is restorable, the fault is restored, or else, the system enters into single computer state. The system has simple structure and reliable signal transmission; the method is easy to control, the system fault rate is greatly reduced, thus having good fault-tolerant effect.