  We report a systematic determination of the responses of PandaX-II, a dual
phase xenon time projection chamber detector, to low energy recoils. The
electron recoil (ER) and nuclear recoil (NR) responses are calibrated,
respectively, with injected tritiated methane or $^{220}$Rn source, and with
$^{241}$Am-Be neutron source, within an energy range from $1-25$ keV (ER) and
$4-80$ keV (NR), under the two drift fields of 400 and 317 V/cm. An empirical
model is used to fit the light yield and charge yield for both types of
recoils. The best fit models can well describe the calibration data. The
systematic uncertainties of the fitted models are obtained via statistical
comparison against the data.
