  We present an extended study of the Be/X-ray pulsar 2S 1553-542 during its
Type II outbursts. We have incorporated \emph{NICER, Swift-XRT, RXTE-PCA,
\emph{NuSTAR} and FERMI} observations to carry out the detailed phase and time
resolved spectral analysis of the source. We have summarized the evidence of
variability of the cyclotron feature observed in the X-ray continuum of the
source with respect to the pulse phases of the pulsar by using the recent
\emph{NuSTAR} observation of 2021 outburst of the source. The time resolved
spectral analysis has been performed by considering \emph{RXTE} observations of
the 2008 outburst of the pulsar. The hardness intensity diagram (HID) has been
obtained using 2008 observations in which the intensity follows distinct
branches with respect to the hardness ratio. Diagonal branch is observed in the
high intensity state whereas the horizontal branch corresponds to the low
intensity state. The transition from the diagonal to horizontal branch occurs
at the luminosity of $(4.88\pm0.24)\;\times\;10^{37}\;erg\;s^{-1}$. The
photon-index exhibits a weak positive correlation with flux along the diagonal
branch and negative correlation along the horizontal branch. The existence of
two different diagonal and horizontal branches further reflects the possibility
of two different accretion states separated by the critical luminosity. The
spin-up rate during the outburst phase is found to depend on the flux and is
found to increase with an increase in flux.
