In the daily process of manufacturing and testing electric motors, the interturn insulation monitoring of marine generator rotor winding is easy to be ignored due to its low voltage and small current, the simpler structure than the stator, also the standards such as IEC60034 and IEC60092 which International Electrotechnical Commission issued have no explicit requirement. However, based on the reliability of product’s quality and function, it is necessary to test the rotor interturn voltage, especially to the interturn insulation monitoring of highvoltage generator rotor winding in order to demonstrate a satisfactory withstand level of the interturn insulation to steep fronted switching surges. The article take the highvoltage generator rotor winding interturn test as an example, introducing the test methods, the failure phenomenon and abnormal analysis, including the problem of judging the insulation abnormal on generator rotor part by pulse waveform, and earth resistance in the manufacturing process.