The Jiangmen Underground Neutrino Observatory (JUNO) is under construction in China to mainly determine the neutrino mass hierarchy (MH) by detecting reactor anti-neutrinos. JUNO consists of central detector, veto detector and calibration system. Its central detector is a 20 kton liquid scintillator (LS) detector and its calibration system is designed to measure the energy of neutrinos with an unprecedented energy resolution of 3% @1MeV and an energy nonlinearity better than 1%. Veto detector, consisting of water Cherenkov detector and top tracker, is used to maximally remove the background events due to cosmic-rays. Due to its large scale and best performance, JUNO will be an exceptional multipurpose detector with rich physical potentials, such as precise measurements of neutrino oscillation parameters, geo-neutrinos, astrophysical neutrinos, sterile neutrinos, dark matter searches, proton decay and other exotic searches.