Abstract: In view of safety problem existed in monitoring and control system for ventilator that uses a single PLC to control operation, a scheme of software redundancy composed by two PLCs was proposed in the paper. One PLC is used as master station, controls the ventilator control system, and carries out non-redundant program which does not need data synchronization process and completes redundancy program of control functions, alarm, analog; and the other PLC is used as reserve station to perform only non-redundancy program. The application of PLC software redundancy system improves reliability of monitoring and control system for ventilator, and meets needs of safety production.