  We report the detection of a strong thermal component in the short Gamma-Ray
Burst 170206A with three intense pulses in its light curves, throughout which
the fluxes of this thermal component exhibit fast temporal variability same as
that of the accompanying non-thermal component. The values of the time-resolved
low-energy photon index in the non-thermal component are between about -0.79
and -0.16, most of which are harder than -2/3 excepted in the synchrotron
emission process. In addition, we found a common evolution between the thermal
component and the non-thermal component, $E_{\rm p,CPL} \propto kT_{\rm
BB}^{0.95\pm0.28}$, and $F_{\rm CPL} \propto F_{\rm BB}^{0.67\pm0.18}$, where
$E_{\rm p,CPL}$ and $F_{\rm CPL}$ are the peak photon energy and corresponding
flux of the non-thermal component, and $ kT_{\rm BB}$ and $F_{BB}$ are the
temperature and corresponding flux of the thermal component, respectively.
Finally, we proposed that the photospheric thermal emission and the
Comptonization of thermal photons may be responsible for the observational
features of GRB 170206A.
