The invention relates to a transmitter monitoring system which operates in a dual-redundancy mode. Two monitoring units are simultaneously powered up to operate and one monitoring unit is in an operating condition and the other monitoring unit is in a standby state. The transmitter monitoring system can receive a control command from a central computer to determine the online monitoring unit. Further, when the online monitoring unit detects its own failure, the standby monitoring unit can be automatically switched to be in an online working state. Thus, a problem is solved that a transmitter subsystem cannot work normally when a single transmitter monitoring unit generates a fault.