  We present modeling of the long-term optical light curve and radial velocity
curve of the binary stellar system CXOGBS J175553.2-281633, first detected in
X-rays in the \textit{Chandra} Galactic Bulge Survey. We analyzed 7 years of
optical I-band photometry from OGLE and found long-term variations from year to
year. These long-term variations can most likely be explained with by either
variations in the luminosity of the accretion disk or a spotted secondary star.
The phased light curve has a sinusoidal shape, which we interpret as being due
to ellipsoidal modulations. We improve the orbital period to be $P = 10.34488
\pm 0.00006$ h with a time of inferior conjunction of the secondary star $T_0 =
{\rm HJD\ } 2455260.8204 \pm 0.0008$. Moreover, we collected 37 spectra over 6
non-consecutive nights. The spectra show evidence for an evolved K7 secondary
donor star, from which we obtain a semi-amplitude for the radial velocity curve
of $K_2 = 161 \pm 6 $ km s$^{-1}$. Using the light curve synthesis code {\tt
XRbinary}, we derive the most likely orbital inclination for the binary of $i =
63.0\pm0.7$ deg, a primary mass of $M_1 = 0.83 \pm 0.06$ M$_\odot$, consistent
with a white dwarf accretor, and a secondary donor mass of $M_2 = 0.65 \pm
0.07$ M$_\odot$, consistent with the spectral classification. Therefore, we
identify the source as a long orbital period cataclysmic variable star.
