  JUNO is a 20-kton liquid scintillator detector aiming to determine the
neutrino mass ordering, precisely measure the oscillation parameters, detect
the astrophysical neutrinos and search for exotic physics. It is designed to
reach an energy resolution of 3% at 1 MeV with the highest ever PMT coverage,
using two types of 20 inch phototubes: MCP-PMT from NNVT and dynode-PMT from
Hamamatsu. In this article, the gain and charge response of the MCP and dynode
PMTs are investigated with the study of JUNO Central Detector prototype. The
linearity of the MCP-PMT charge output is measured too to check the effect of a
long tail on its charge spectrum.
