Abstract: The reliability of converters is significant for wind energy conversion systems.However,the effect of junction temperature fluctuation is not valued by present papers when evaluating reliability of converters in wind turbines based on junction temperature of devices.As a result,it is often overestimated.Based on bad operating environments of permanent magnetism synchronous generators（PMSGs）,the change of the cutting in wind speed,the rated wind speed,the cutting out wind speed,the switching frequency and the power factor,leading to the difference of junction temperature and its’ fluctuation of devices,was considered in the paper,and the Coffin-Manson reliability evaluation model was used to evaluate the difference of reliability of converters in the grid side.Then,consideried the actual wind speed,a 1 MW wind turbine was illustrated.The test results verified the correctness of the theoretical analysis.The result indicates that the change of rated wind speed and switching frequency has a significant effect on converters’ reliability.To get high reliability of converters,it is suggested that the wind turbine would better cut in with a low wind speed and cut out with a high wind speed possible.