  In the manuscript, a 3.8yr optical quasi-periodic oscillations (QPOs) is
reported in blue quasar SDSS J132144+033055 (=\obj) at $z=0.269$, based on
16.3yr-long light curve from both CSS and ZTF directly described by a
sinusoidal function. The 3.8yr QPOs can be confirmed through the Generalized
Lomb-Scargle periodogram with confidence level higher than 5$\sigma$, through
properties of the phase-folded light curve and the WWZ technique. Moreover, the
collected Pan-STARRS light curves well follow the sinusoidal function described
best fitting results to the CSS and ZTF light curves. The optical QPOs strongly
indicate a central binary black hole (BBH) system in \obj, with expected space
separation smaller than 0.018pc, through the estimated upper limit of total BH
mass $3.3\times10^9{\rm M_\odot}$ through the correlation between BH mass and
continuum luminosity. Meanwhile, we check disk precession applied to explain
the optical QPOs. However, under the disk precession assumption, the determined
optical emission regions from central BH have sizes about $37{\rm R_G}$ similar
as the sizes $35{\rm R_G}$ of the expected NUV emission regions through the
correlation between disk size and BH mass, indicating the disk precession is
not preferred. And due to undetected radio emissions, jet precession can be
ruled out. Furthermore, only 0.1\% probability can determined as the QPOs
mis-detected through CAR process randomly created light curves related to
intrinsic AGN activities, re-confirming the optical QPOs with significance
level higher than 3$\sigma$. Therefore, combining long-term light curves from
CSS and ZTF can lead to more QPOs candidates in the near future.
