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 2017 January using the Nanshan One-meter Wide-field Telescope to search for variable stars in the field of the cluster. 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 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 mag eclipse in its light curve.