  This work presents the charge-coupled device (CCD) photometric survey of the
old open cluster NGC 188. Time-series V-band photometric observations were
conducted for ten nights in January 2017 using the Nanshan One-meter Wide-field
Telescope (NOWT) to search for variable stars in the field of the cluster
field. A total of 25 variable stars, including one new variable star, were
detected in the target field. Among the detected variables, 16 are cluster
member stars, and the others are identified as field stars. The periods, radial
velocities, effective temperatures, and classifications of the detected
variables are discussed in this work. Most of the stars' effective temperatures
are between 4200 K and 6600 K, indicating their spectral types are G or K. The
newly discovered variable is probably a W UMa system. In this study, a known
cluster variable star (V21 = V0769 Cep) is classified as an EA-type variable
star based on the presence of an 0.5 magnitude eclipse in its light curve.
