  3C 454.3 is frequently observed in flaring state. The long term light curve
of this source has been analysed with 9 year (August 2008 - July 2017) data
from Fermi LAT detector. We have identified five flares and one quiescent
state. The flares have sub-structures with many peaks during flaring phase. We
have estimated the rise and decay time of the flares and compared with flares
of other similar sources. The modeling of gamma ray spectral energy
distributions shows in most cases Log parabola function gives the best fit to
the data. We have done time dependent leptonic modeling of two of the flares,
for which simultaneous multi-wavelength data are available. These two long
lasting flares Flare-2A and Flare-2D continued for 95 days and 133 days
respectively. We have used the average values of Doppler factor, injected
luminosity in electrons, size of the emission region and the magnetic field in
the emission region in modeling these flares. The emission region is assumed to
be in the broad line region in our single zone model. The energy losses
(synchrotron, synchrotron self-Compton, external Compton) and escape of
electrons from the emission region have been included while doing the
modelling. Although, the total jet powers required to model these flares with
leptonic model are higher compared to other sources, they are always found to
be lower than the Eddington's luminosity of 3C 454.3. We also select some
flaring peaks and show that time variation of the Doppler factor or the
injected luminosity in electrons over short time scales can explain their light
curves.
