The trigger amplifier of a radar transmitter provides a discharge trigger for Silicon Controlled Rectifiers (SCRs) and protects itself from being damaged. The diagnosis procedures of the trigger amplifier is described, which locates faults to the chip level of the unit and lowers the expenses of hardware maintenance, and provides the technical support in the autodiagnostic model on the radar test platform. The standardized diagnosis procedures of the trigger amplifier are based on the trigger signal flow, the measurements of pulse waves and voltages of the key points, as well as the causal relationship of the fault tree diagram. An example is given, in which minus 200 voltages did not appear because of the lack of trigger output. The results show that the procedures are useful for finding the fault chips in the trigger amplifier, easy to learn for the radar technique personnel, and effective for improving the availability ratio of the radar system.