IGBT junction temperature fluctuation is one of the important factors affecting the accuracy of IGBT life evaluation of photovoltaic inverters. This paper proposes a lifetime evaluation method for photovoltaic inverters that considers the influence of fundamental frequency/low frequency junction temperature. Firstly, the junction temperature profile is divided into different time scales. The physical characteristics of the fundamental frequency junction temperature and the low frequency junction temperature were compared and analyzed. Secondly, the calculation range of the junction temperature fluctuation frequency in the IGBT lifetime evaluation process was expanded, and the corresponding photovoltaic inverter IGBT electro-thermal model and lifetime model were established to quantitatively analyze the influence of fundamental frequency/low frequency junction temperature on the lifetime evaluation of photovoltaic inverters. Finally, taking different latitude regions as examples, the life damage of photovoltaic inverters under different mission profiles and different sampling periods is evaluated. The results show that the method comprehensively considering the influence of fundamental frequency/low frequency junction temperature can effectively improve the accuracy of lifetime evaluation of photovoltaic inverters, which is helpful to guide the operation and maintenance of photovoltaic inverters, and reduce economic losses caused by unplanned shutdowns.