  The GeV break in spectra of the blazar 3C 454.3 is a special observation
feature that has been discovered by the {\it Fermi}-LAT. The origin of the GeV
break in the spectra is still under debate. In order to explore the possible
source of GeV spectral break in 3C 454.3, a one-zone homogeneous leptonic jet
model, as well as the {\it McFit} technique are utilized for fitting the
quasi-simultaneous multi-waveband spectral energy distribution (SED) of 3C
454.3. The outside border of the broad-line region (BLR) and inner dust torus
are chosen to contribute radiation in the model as external, seed photons to
the external-Compton process, considering the observed $\gamma$-ray radiation.
The combination of two components, namely the Compton-scattered BLR and dust
torus radiation, assuming a broken power-law distribution of emitted particles,
provides a proper fitting to the multi-waveband SED of 3C 454.3 detected 2008
Aug 3 - Sept 2 and explains the GeV spectral break. We propose that the
spectral break of 3C 454.3 may originate from an inherent break in the energy
distribution of the emitted particles and the Klein-Nishina effect. A
comparison is performed between the energy density of the 'external' photon
field for the whole BLR $U_{\rm BLR}$ achieved via model fitting and that
constrained from the BLR data. The distance from the position of the
$\gamma$-ray radiation area of 3C 454.3 to the central black hole could be
constrained at $\sim 0.78$pc ($\sim 4.00 R_{\rm BLR}$, the size of the BLR).
