  LHAASO-WCDA is a large ground-based water Cherenkov detector array planned to
be built at Shangri-La, Yunnan Province, China. As a major component of LHAASO
project, the main purpose of LHAASO-WCDA is to survey the northern sky for
very-high-energy (above 100 GeV) gamma ray sources. To gain full knowledge of
water Cherenkov technique and to well investigate engineering issues, a 9-cell
detector array has been built at Yang-Ba-Jing site, neighboring to the ARGO-YBJ
experiment. With the array, charge calibration methods for low and high ranges
of the PMT readout are studied, whose result shows that a very high precision
at several percentages can be reached. These calibration methods are proposed
to be applied in the future LHAASO-WCDA project.
