The Jiangmen Underground Neutrino Observatory (JUNO) is the state of the art, liquid scintillator (LS) based, large neutrino detector. Due to the large 20 kt LS target mass with the tight requirements on its optical and radio-purity properties, it will be able to perform leading measurements detecting reactor, terrestrial and astrophysical neutrinos. Central detector (CD) of JUNO adopts the scheme of a spherical acrylic vessel with stainless steel (SS) structure immersed in pure water. LS will be contained by CD with an inner diameter of 35.4 m and a thickness of 120 mm. The acrylic vessel is transparent for scintillation lights to pass through and then be detected by PMTs mounted on SS and followed by underwater electronics. Since 2014, the key technologies of acrylic have been successfully developed, such as low radioactivity and high transmittance manufacturing technology of acrylic panels, tensile and compressive acrylic node design with embedded stainless steel, etc. During R&D process, many technical challenges of SS were solved, such as low radioactive SS material, deformation and precision control, high strength SS rivet bolt, etc. A FOC system was designed to realize the functions of filling, overflow, and circulation of LS in CD. At present, the onsite installation has been started at the end of 2021. The installation of SS structure will be completed in 2022, the detector construction will end in 2023.