The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose physics underground experiment in southern China. Its central detector mainly consists of a 20-kton liquid scintillator and 17,612 20-inch photomultiplier tubes. A dedicated multi-messenger trigger system has been developed to maximize JUNO’s potential for astrophysics events, lowering the data-taking threshold to around 20 keV. The currently existing calibration sources for JUNO are envisioned to be deployed to calibrate the MeV energy range, and hence new radioactive sources as well as calibration strategy are necessary to calibrate the sub-MeV range (from O(10) to O(100) keV). For this purpose, Radium-226 (186 keV gamma-ray) and Americium-241 (59.5 keV gamma-ray) are considered as primary radioactive calibration sources. This proceedings paper describes the calibration feasibility in this very low-energy range including impacts on the calibration quality due to the source apparatus geometry, separation from Carbon-14 backgrounds using the JUNO detector simulation tool, and also introduces the status of the low-energy calibration source preparation.