  In this paper, we perform a comprehensive study for the physical properties
of SN 2018gk which is a luminous type IIb supernova (SN). We find that the
early-time photospheric velocity vary from a larger value to a smaller value
before the photosphere reach a temperature floor. We generalize the photosphere
modulus and fit the multi-band light curves (LCs) of SN 2018gk. We find that
the $^{56}$Ni mass model require $\sim0.90$ M$_\odot$ of $^{56}$Ni which is
larger than the derived ejecta mass ($\sim0.10$ M$_\odot$). Alternatively, we
use the magnetar plus $^{56}$Ni and the fallback plus $^{56}$Ni models to fit
the LCs of SN 2018gk, finding that the two models can fit the LCs. We favor the
magnetar plus $^{56}$Ni since the parameters are rather reasonable ($M_{\rm ej}
=1.65$ M$_\odot$, $M_{\rm Ni}=0.05$ M$_\odot$ which is smaller than the upper
limit of the value of the $^{56}$Ni mass can by synthesized by the
neutrino-powered core collapse SNe $B=6.52\times10^{14}$ G which is comparable
to those of luminous and superluminous SNe studied in the literature, and
$P_0=10.42$ ms which is comparable to those of luminous SNe), while the
validity of the fallback plus $^{56}$Ni model depends on the accretion
efficiency ($\eta$). Therefore, we suggest that SN 2018gk might be a SN IIb
mainly powered by a central engine. Finally, we confirm the NIR excesses of the
spectral energy distributions (SEDs) of SN 2018gk at some epochs and constrain
the physical properties of the putative dust using the blackbody plus dust
emission model.
