  GRB 090618 was simultaneously detected by Swift-BAT and Fermi-GBM. Its light
curve shows two emission episodes consisting of four prominent pulses. The
pulse in the first episode (episode A) has a smoother morphology than the three
pulses in the second episode (episode B). Using the pulse peak-fit method, we
have performed a detailed analysis of the temporal and spectral characteristics
of these four pulses and found out that the first pulse (pulse A) exhibits
distinctly different properties than the others in episode B (pulses B1, B2 and
B3) in the following aspects. (i) Both the pulse width ($w$) and the
rise-to-decay ratio of pulse ($r/d$, pulse asymmetry) in GRB 090618 are found
to be energy-dependent. The indices of the power-law correlation between $w$
and $E$ for the pulses in episode B however are larger than that in episode A.
Moreover the pulses B1, B2 and B3 tend to be more symmetric at the higher
energy bands while the pulse A displays a reverse trend. (ii) Pulse A shows a
hard-to-soft spectral evolution pattern, while the three pulses in the episode
B follow the light curve trend. (iii) Pulse A has a longer lag than the pulses
B1, B2 and B3. The mechanism which causes the different pulse characteristics
within one single GRB is unclear.
