  A model-dependent method is proposed to determine the location of the
$\gamma$-ray emitting region for a given flat spectrum radio quasar (FSRQ). In
the model, the extra-relativistic electrons are injected at the base of the jet
and non-thermal photons are produced by both synchrotron radiation and
inverse-Comtpon (IC) scattering in the energy dissipation region. The target
photons dominating inverse-Comtpon scattering originate from both synchrotron
photons and external ambient photon fields, and the energy density of external
radiation field is a function of the distance between the position of
dissipation region and a central super-massive black hole, and their spectra
are seen in the comoving frame. Moreover, the energy dissipation region could
be determined by the model parameter through reproducing the $\gamma$-ray
spectra. Such a model is applied to reproduce the quasi-simultaneous
multi-wavelength observed data for 36 FSRQs. In order to define the width of
the broad-line region shell and dusty molecular torus shell, a simple numerical
constraint is used to determine the outer boundary of the broad-line region and
dusty molecular torus. Our results show that 1) the $\gamma$-ray emitting
regions are located at the range from 0.1 pc to 10 pc; 2) the $\gamma$-ray
emitting regions are located outside the broad-line regions and within the
dusty molecular tori; and 3) the $\gamma$-ray emitting region are located
closer to the dusty molecular torus ranges than the broad-line regions.
Therefore, it may concluded that a direct evidence for the \emph{far site}
scenario could be obtained on the basis of the model results.
