  1RXS J201607.0251645 is identified to be an eclipsing binary for the first
time. We present the preliminary observations in V band with the 0.6-m
telescope for three years and the extensive observations in V and R band with
the 0.8-m telescope for six nights respectively. The light curve of the system
is EB type. Five light minimum times were obtained and the orbital period of
0.388058d(0.00044d) is determined. The photometric solution given by the
2003-version Wilson-Devinney program suggests the binary is a semi-detached
system with the photometric mass ratio 0.895(0.006), which probably comprise a
G5 primary and an oversize K5 secondary. The less massive component has
completely filled up its Roche lobe, while the other almost fills its Roche
lobe with the filling factor of 93.4%. The system shows a varying O'Connell
effect in its phase folded diagrams from 2005 to 2007, and is X-ray luminous
with log(LXLbol)3.27. Possible mechanisms to account for these two phenomena
are discussed. Finally, we infer the binary may be in thermal oscillation
predicted by thermal relaxation oscillation (TRO) theory or may evolve into a
contact binary.
