The relativistic (~500 keV–2 MeV) and ultra-relativistic (~> 2 MeV) electron three-belt structure can originate from the partial depletion of the preexisting outer belt and replenishment of the new belt without direct electron injections. These processes may be related to radial diffusion caused by ULF (Ultra-Low Frequency) waves and local acceleration by VLF (Very-Low Frequency) waves. In this study, we reported a three-belt event with several hundred keV electrons based on Arase observation. The partial depletion of the outer belt and subsequent formation of a new belt due to source and seed electron (~30–500 keV) injection may be the primary mechanisms responsible for the three-belt structure. This discovery showed that the three-belt structure might not be limited to relativistic and ultra-relativistic electrons. Our study provided evidence for the existence of the source and seed electron three-belt structure, which could help improve our understanding of the radiation belt configuration.