  We explore the explanation of the Fermi Galactic Center Excess (GCE) in the
Next-to-Minimal Supersymmetric Standard Model. We systematically consider
various experimental constraints including the Dark Matter (DM) relic density,
DM direct detection results and indirect searches from dwarf galaxies. We find
that, for DM with mass ranging from $30 {\rm GeV}$ to $40 {\rm GeV}$, the GCE
can be explained by the annihilation $\chi \chi \to a^\ast \to b \bar{b}$ only
when the CP-odd scalar satisfies $m_a \simeq 2 m_\chi$, and in order to obtain
the measured DM relic density, a sizable $Z$-mediated contribution to DM
annihilation must intervene in the early universe. As a result, the higgsino
mass $\mu$ is upper bounded by about 350 GeV. Detailed Monte Carlo simulations
on the $3\ell+ E_T^{miss}$ signal from neutralino/chargino associated
production at 14-TeV LHC indicate that the explanation can be mostly
(completely) excluded at $95\%$ C.L. with an integrated luminosity of 100(200)
fb$^{-1}$. We also discuss the implication of possible large $Z$ coupling to DM
for the DM-nucleon spin dependent (SD) scattering cross section, and find that
although the current experimental bounds on $\sigma^{\rm SD}_p$ is less
stringent than the spin independent (SI) results, the future XENON-1T and LZ
data may be capable of testing most parts of the GCE-favored parameter region.
