  We present a detailed analysis of the observations with the Hard X-ray
Modulation Telescope of the black hole X-ray transient 4U~1543-47 during its
outburst in 2021. We find a clear state transition during the outburst decay of
the source. Using previous measurements of the black-hole mass and distance to
the source, the source luminosity during this transition is close to the
Eddington limit. The light curves before and after the transition can be fitted
by two exponential functions with short ($\sim 16$ days) and long ($\sim 130$
days) decay time scales, respectively. We detect strong reflection features in
all observations that can be described with either the RelxillNS or Reflionx_bb
reflection models, both of which have a black-body incident spectrum. In the
super-Eddington state, we observe a Comptonized component characterized by a
low electron temperature of approximately 2.0 keV. We suggest that this
component appears exclusively within the inner radiation-pressure dominated
region of the supercritical disk as a part of the intrinsic spectrum of the
accretion disk itself. This feature vanishes as the source transitions into the
sub-Eddington state. The emissivity index of the accretion disk in the
reflection component is significantly different before and after the
transition, $\sim3.0$-$5.0$ and $\sim7.0$-$9.0$ in the super- and sub-Eddington
states, respectively. Based on the reflection geometry of returning disk
radiation, the geometrically thicker the accretion disk, the smaller the
emissivity index. Therefore, we propose that the transition is primarily driven
by the change of the accretion flow from a supercritical to a thin disk
configuration.
