  Stellar activity cycles reveal continuous relaxation and induction of
magnetic fields. The activity cycle is typically traced through the observation
of cyclic variations in total brightness or Ca H&K emission flux of stars, as
well as cyclic variations of orbital periods of binary systems. In this work,
we report the identification of a semi-detached binary system (TIC 16320250)
consisting of a white dwarf (0.67 $M_{\odot}$) and an active M dwarf (0.56
$M_{\odot}$). The long-term multi-band optical light curves spanning twenty
years revealed three repeated patterns, suggestive of a possible activity cycle
of about ten years of the M dwarf. Light curve fitting indicates the repeated
variation is caused by the evolution, particularly the motion, of polar spots.
The significant Ca H&K, H$\alpha$, ultra-violet, and X-ray emissions imply that
the M dwarf is one of the most magnetically active stars. We propose that in
the era of large time-domain photometric sky surveys (e.g., ASAS-SN, ZTF, LSST,
Sitian), long-term light curve modeling can be a valuable tool for tracing and
revealing stellar activity cycle, especially for stars in binary systems.
