  The quality of PMT signal is one of the key items for a large and high
precision neutrino experiment, like Daya Bay, JUNO, while most of the
experiments are affected by the PMT signal overshoot from its positive
HV-single cable scheme. For JUNO prototype detector, we have a detailed study
on the PMT overshoot and successfully reduced the ratio of overshoot amplitude
to signal to ~1% from previous typical ~10%, with no affection to PMT other
parameters. Furthermore, we calculated that the overshoot is a result of
discharging of capacitors in the HV-signal splitter and the PMT voltage
divider. The study result is extremely important for JUNO and other similar
experiments.
