  Owing to narrow energy band of \textit{Swift}/BAT, several urgent issues are
required to pay more attentions but unsolved so far. We systematically study
the properties of a refined sample of 283 \textit{Swift}/BAT gamma-ray bursts
with well-measured spectral peak energy ($E_{\text p}$) at a high confidence
level larger than 3$\sigma$. It is interestingly found that duration ($T_{90}$)
distribution of \textit{Swift} bursts still exhibits an evident bimodality with
a more reliable boundary of $T_{90}\simeq$1.06 s instead of 2 s for previously
contaminated samples including bursts without well-peaked spectra, which is
very close to $\sim$1.27 s and $\sim$0.8 s suggested by some authors for
Fermi/GBM and \textit{Swift}/BAT catalogs, respectively. The \textit{Swift}/BAT
short and long bursts have comparable mean $E_{\text p}$ values of
$87^{+112}_{-49}$ and $85^{+101}_{-46}$ keV in each, similar to what found for
both types of BATSE bursts, which manifests the traditional
short-hard/long-soft scheme may not be tenable for the certain energy window of
a detector. In statistics, we also investigate the consistency of distinct
methods for the $E_{\text p}$ estimates and find that Bayesian approach and
BAND function can always give consistent evaluations. In contrast, the
frequently-used cut-off power-law model matches two other methods for lower
$E_{\text p}$ and will overestimate the $E_{\text p}$ more than 70\% as
$E_{\text p}>$100 keV. Peak energies of X-ray flashes, X-ray rich bursts and
classical gamma-ray bursts could have an evolutionary consequence from
thermal-dominated to non-thermal-dominated radiation mechanisms. Finally, we
find that the $E_{\text p}$ and the observed fluence ($S_{\gamma}$) in the
observer frame are correlated as $E_p\simeq [S_{\gamma}/(10^{-5} erg\
cm^{-2})]^{0.28}\times 117.5^{+44.7}_{-32.4}$ keV proposed to be an useful
indicator of GRB peak energies.
