  We select 52 long gamma-ray bursts(GRBs) having the precursor activity in the
third Swift-BAT catalog. Each episode shown in both the precursors and the main
bursts is fitted by the Norris function. We systematically analyze the temporal
properties for both the precursors and the main bursts. We do not find any
significant difference between the temporal profile of the precursor and that
of the main burst. The photon count of the precursor is related to that of the
main burst. It is indicated that the precursor and the main burst might have
the same physical origin, as the precursor and the main burst follow the same
$\tau_p-\omega$ relation. However, we do not find the explicit relation between
the energy release of the precursor and the quiescent time. Some theoretical
models, such as the fallback collapsar scenario and the jet-cocoon scenario,
may be helpful to explain the GRB-precursor phenomena.
