  Owing to lack of multiple components of prompt $\gamma$-ray emissions in
short gamma-ray bursts (sGRBs), how these distinct components are correlated
still keeps unclear. In this paper, we investigate the spectral and temporal
properties of precursors, main peaks and extended emissions in 26 sGRBs
including GRB 170817A. It is found that peak energies ($E_p$) in each pulse are
uncorrelated with the pulse duration ($t_{dur}$). Meanwhile, we find that there
is no obvious correlation between peak energy and energy fluence.
Interestingly, there is no obvious spectral evolution from earlier precursors
to later extended emissions in view of the correlations of $t_{dur}$ with
either the $E_p$ or the low energy spectrum index, $\alpha$. A power-law
correlation between the average flux ($F_{p}$) and the energy fluence
($S_\gamma$), $log F_p=(0.62\pm0.07) log S_\gamma + (0.27\pm0.07)$, is found to
exist in the individual segments instead of mean peaks previously. Furthermore,
we also find that the main peaks are on average brighter than the precursors or
the extend emissions about one order of magnitude. On the basis of all the
above analyses, one can conclude that three emissive components would share the
same radiation mechanisms but they might be dominated by diverse physical
processes.
