Under variable wind speed operation, the power modules of wind power converters suffered different time-scales of junction temperature variations; long-term junction temperature variation caused by wind speed and short-term variation caused by working commutation. In order to generally estimate the reliability effect of long-term and short-term junction temperature, a multi-time scales reliability evaluation model has been developed in this article. As with long-term junction temperature variation, thermal factor and thermal cycling factors have been introduced based on FIDES guide and the effect of wind speed and wind turbulence have been evaluated. As with short-term junction temperature variation, multi-states evaluation philosophy have been adopted, and the wind speed distribution has been allotted to address the different effect to power module reliability. Finally, taking a real field wind power converter as example, the reliability has been assessed and the effects of design parameters have been analyzed. The achievement of this research would prove useful reference for the enhancement of wind power converter reliability.