The Jiangmen Underground Neutrino Observatory (JUNO) is designed to primarily measure the neutrino Mass Hierarchy. Its Central Detector (CD), which is made of 20 kton Liquid Scintillator (LS), about 18000 20-inch PMTs and 36000 3-inch PMTs, will be the largest LS detector to achieve an unprecedented energy resolution of 3% @1MeV and an energy nonlinearity better than 1%. In the meanwhile, an acrylic spherical shell with a diameter of 35.4m and a stainless steel-latticed shell with a diameter of 40.1m will be constructed for LS container and PMT deployment respectively. Furthermore, a calibration complex is designed for multiple source deployment, the energy coverage of reactor neutrinos and CD full-volume coverage. In this proceeding, the design details and primary progress about the central detector and its calibration system are presented.