Cao Jun has been working on Daya Bay Reactor Neutrino Experiment since 2003 and now is the co-spokesperson. He was one of the initiators of the experiment and contributed the major efforts in the experiment design. He led the neutrino detector design and fabrication, as well as the liquid scintillator production. Cao led the data analysis of Daya Bay, which measured the smallest neutrino mixing angle theta13 in early 2012 and opened a gateway to the future study of CP violation in neutrino oscillation.