  N-body simulations predict that galaxies at the Milky Way scale host a large
number of dark matter (DM) subhalos. Some of these subhalos, if they are
massive enough or close enough to the Earth, might be detectable in $\gamma$
rays due to the DM annihilation. 3FGL J2212.5+0703, an unidentified gamma-ray
source, has been suggested to be the counterpart candidate of a DM subhalo by
Bertoni et al. (2015, 2016). In this work we analyze the Fermi-LAT Pass 8 data
of 3FGL J2212.5+0703 to independently test the DM subhalo hypothesis of this
source. In order to suppress the possible contamination from two nearby
very-bright blazars, we just take into account the front-converting gamma-rays
which have better angular resolutions than that of the back-converting photons.
In addition to the spatial distribution analysis, we have extended the spectrum
analysis down to the energies of $\sim 100$ MeV, and thoroughly examined the
variability of the emission during the past 8 years. We confirm that 3FGL
J2212.5+0703 is a steady and spatially-extended gamma-ray emitter at a high
confidence level. The spectrum is well consistent with that expected from DM
annihilation into $b\bar{b}$. The introduction of a phenomenological
LogParabola spectrum just improves the fit slightly. All these results suggest
that 3FGL J2212.5+0703 could be indicative of a DM subhalo.
