  The growing observed evidence shows that the long- and short-duration
gamma-ray bursts (GRBs) originate from massive star core-collapse and the
merger of compact stars, respectively. GRB 201221D is a short-duration GRB
lasting $\sim 0.1$ s without extended emission (EE) at high redshift $z=1.046$.
By analyzing data observed with the Swift/BAT and Fermi/GBM, we find that a
cutoff power-law model can adequately fit the spectrum with a soft $E_{\rm
p}=113^{+9}_{-7}$ keV, and isotropic energy $E_{\gamma,iso}
=1.36^{+0.17}_{-0.14}\times 10^{51}~\rm erg$. In order to reveal the possible
physical origin of GRB 201221D, we adopted multi-wavelength criteria (e.g.,
Amati relation, $\varepsilon$-parameter, amplitude parameter, local event rate
density, luminosity function, and properties of the host galaxy), and find that
most of the observations of GRB 201221D favor a compact star merger origin.
Moreover, we find that $\hat{\alpha}$ is larger than $2+\hat{\beta}$ in the
prompt emission phase which suggests that the emission region is possibly
undergoing acceleration during the prompt emission phase with a
Poynting-flux-dominated jet.
