Abstract: The power line emission (PLE) generated by the ground power system observed by satellite has attracted much attention in recent years. To enhance the precision in identifying and researching the PLE phenomenon in the topside ionosphere, the study of the spatiotemporal distribution characteristics of the power frequency electric field background noise is also crucial. This study used extremely low frequency (ELF) electric field data collected by the China Seismo-Electromagnetic Satellite (CSES) from 2019 to 2021 to analyze the spatiotemporal variation characteristics of 50/60Hz ionospheric electric field background noise at 2:00LT during the night and 14:00LT during the day. It is found that the global power frequency electric field background noise mainly comes from bottom-up lightning activity. In areas with high lightning density, the ionospheric power frequency electric field background noise is strong, and the night side is much larger than the day side, and the correlation with geomagnetic activity is weak. In addition, in areas with high lightning density, the power frequency electric field background has obvious periodic variation characteristics; in areas with low lightning density, the periodic variation of the power frequency electric field background is not significant. The temporal and spatial distribution of the ionospheric power frequency background noise is affected not only by the intensity of the source and the electron density of the lower ionosphere, but also by the configuration of the geomagnetic field. The higher the magnetic latitude, the easier it is for lightning signals to enter the ionosphere. Therefore, the ionospheric power frequency background noise will have complex variation characteristics in time such as the year and season, and in space such as latitude and longitude.