  Context.Unusually, there are still certain characteristics of the
changing-look (CL) active galactic nuclei (AGNs) that remain
undetected.Consequently,the trigger mechanism behind the CL phenomenon observed
in partial AGNs remains unknown.Aims.We explore the light curve and spectral
energy distribution (SED) of the CL blazar OQ 334 as obtained by Fermi-LAT.
Methods. By examining the variability of the equivalent width (EW), we
categorise the Fermi-LAT light curves of OQ 334 during the epoch of MJD
54628-58677 into seven distinct epochs, including the flat spectrum radio
quasar (FSRQ) state, the transition state, and the BL Lac state. We obtained
both a Fermi-LAT SED and a multi-wavelength SED for each of these distinct
epochs. Results. The source exhibits a transformation from a quiescent state to
a highly active state, as evidenced by the variability of the EW. The
multi-wavelength SEDs display a prominent external Compton characteristic, even
though the Fermi-LAT SED reveals both a FSRQ and a BL Lac state across the
seven different epochs. To gain further insights, we employed a leptonic model
that takes into account the soft photon fields originating from both
synchrotron radiation and the external environment. By simulating the
multi-wavelength SEDs for each epoch, we uncover the following results.
Firstly, the energy density of the external photon fields evolves in an
oscillatory manner over the seven different epochs. Also, the energy density of
the external photon fields in the BL Lac state is lower than that in the FSRQ
state.Conclusions. These findings suggest that the CL blazar represents a
unique phase in the blazar sequence.
