  As the main detector of the GECAM satellite, the calibration of the energy
response and detection efficiency of the GRD detector is the main content of
the ground-based calibration. The calibration goal requires the calibrated
energy points to sample the full energy range (8 keV-2 MeV) as much as
possible. The low energy band (8-160 keV) is calibrated with the X-ray beam,
while the high energy band (>160 keV) with radioactive sources. This article
mainly focuses on the calibration of the energy response and detection
efficiency in the 8-160 keV with a refined measurement around the absorption
edges of the lanthanum bromide crystal. The GRD performances for different
crystal types, data acquisition modes, working modes, and incident positions
are also analyzed in detail. We show that the calibration campaign is
comprehensive, and the calibration results are generally consistent with
simulations as expected.
