  Magnetic cataclysmic variables (CVs) contain a white dwarf with magnetic
field strong enough to control the accretion flow from a late type secondary.
In this paper, we discover a magnetic CV (CXOGSG J215544.4+380116) from the
$Chandra$ archive data. The X-ray light curves show a significant period of
14.1 ks, and the X-ray spectra can be described by a multi-temperature hot
thermal plasma, suggesting the source as a magnetic CV. The broad dip in the
X-ray light curve is due to the eclipse of the primary magnetic pole, and the
additional dip in the bright phase of the soft and medium bands may be caused
by the accretion stream crossing our line of sight to the primary pole.
Follow-up optical spectra show features of an M2--M4 dwarf dominating the red
band and a WD which is responsible for the weak upturn in the blue band. The
mass ($\sim$ 0.4 $M_{\odot}$) and radius ($\sim$ 0.4 $R_{\odot}$) for the M
dwarf are obtained using CV evolution models and empirical relations between
the orbital period and the mass/radius. The estimated low X-ray luminosity and
accretion rate may suggest the source as a low-accretion-rate polar. In
addition, Very Large Array observations reveal a possible radio counterpart to
the X-ray source, but with a low significance. Further radio observations with
high quality are needed to confirm the radio counterpart and explore the
properties of this binary system.
