The servo system is mainly responsible for receiving radar terminal operator instructions and sending radar signals produced through the drive to control the antenna motion, and meanwhile receiving the instructions from the antennas’ rotating transformer, and sending the quantified information to the signal processing system. If the servo system cannot receive the antenna scanning movement instructions or cannot produce right signals to the driver, the antenna scan will stop. If the radar antenna scans regularly, but the angle data of antenna direction cannot be properly sent to the signal processing system, the linear or ring shaped graphics may be resulted at the radar terminal or a certain layer of scanning may miss in the processing. The causes of servo system failure are analyzed, and some suggestions about the servo system failure diagnosis and troubleshooting are given in combination with two cases of servo system failure, based on the flow, structure, and principles of servo system signals and the waveforms and parameters at key points. Various sorts of servo system failure are classified, aiming to eliminate servo system failure rapidly through accumulated experiences.