The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment in China with a 20-thousand-ton liquid scintillator detector of 3% (at 1 MeV) at 700-meter deep underground. The major goal of JUNO is determining neutrino mass hierarchy by precisely measuring the energy spectrum of reactor electron antineutrinos at a distance of ~53 km from the powerful reactors of the Yangjiang and Taishan Nuclear Power Plants. Also for all 6 neutrino oscillation parameters, JUNO is going to measure the 3 parameters of Δm^2_21, Δm^2_32 and sin^2θ_12 with the precision better than 1% . Considering the precision of sin^2θ_13 can be measured to ~4% by Daya Bay, the unitarity of the neutrino mixing matrix can be probed to 1% level. Besides, JUNO has other scientific possibilities such as supernova neutrinos, geo-neutrinos, solar neutrinos, atmospheric neutrinos, and exotic searches.