Abstract: The redundancy technique is an effective way to increase reliability. This paper deals with the simulation study on a triple redundant flight control system. The redundant system has the capability of fail-operation and employs three "on-line" signal selectors, six "off-line" comparators and an active-standby servomechanism. The signal selector consisted of operational amplifiers. In triplex system the intermediate voltage was selected and transmitted among three input signals. All the failure signals （i. e. hard-overs, null-failures, degraded signals） was isolated and abondoned.In the servoloop, a servo model was used to compare with active-standby servomechanism.The effectiveness of the signal selector, comparator and active-standby servomechanism has been proved by various failure tests of the system. It is shown that their performance and effectiveness are satisfactory. Redundancy management is preferable, but the application of active-standby servomechanism is limited to control functions which will accept small failure transients.