Fly-by-ware is the symbol of modern advanced aircraft.Redundancy is a key means to improve the reliability and safety of fly by wire control system.Some basic concepts on the monitor,the traditional four-redundant control algorithm and a modified four-redundant analog volume monitor algorithm are described in detail.This method can verify the validity of the signal more accurately,can reduce the probability of signal into the multi-fault logic to judge the situation.Simulation have shown that this modified monitor algorithm is rational,reliable and simple.