Charmonium photoproduction at LHC is one of the most promising probes of the gluon density distribution at low Bjorken x. The cross section for the exclusive J/Psi photoproduction has been measured in pp collisions by LHCb and in ultra-peripheral p-Pb and Pb-Pb collisions by the ALICE collaboration. This talk will focus on necessary theoretical inputs, experimental challenges in the extraction of photoproduction cross section at LHC and implications for the study of gluon density distribution and nuclear gluon shadowing from the photoproduction measurements.