  The variability in multi-pulse gamma-ray bursts (GRBs) may help to reveal the
mechanism of underlying processes from the central engine. To investigate
whether the self-organized criticality (SOC) phenomena exist in the prompt
phase of GRBs, we statistically study the properties of GRBs with more than 3
pulses in each burst by fitting the distributions of several observed physical
variables with a Markov Chain Monte Carlo approach, including the isotropic
energy $E_{\rm iso}$, the duration time $T$ and the peak count rate $P$ of each
pulse. Our sample consists of 454 pulses in 93 GRBs observed by the CGRO/BATSE
satellite. The best-fitting values and uncertainties for these power-law
indices of the differential frequency distributions are: $\alpha^d_{E}=1.54 \pm
0.09$, $\alpha^d_{T}=1.82_{-0.15}^{+0.14}$ and
$\alpha^d_{P}=2.09_{-0.19}^{+0.18}$, while the power-law indices in the
cumulative frequency distributions are: $\alpha^c_{E}=1.44_{-0.10}^{+0.08}$,
$\alpha^c_{T}=1.75_{-0.13}^{+0.11}$ and $\alpha^c_{P}=1.99_{-0.19}^{+0.16}$. We
find that these distributions are roughly consistent with the physical
framework of a Fractal-Diffusive, Self-Organized Criticality (FD-SOC) system
with the spatial dimension $S=3$ and the classical diffusion $\beta$=1. Our
results support that the jet responsible for the GRBs should be magnetically
dominated and magnetic instabilities (e.g., kink model, or tearing-model
instability) lead the GRB emission region into the SOC state.
