  We study the $B$ meson radiative decay $B \to X_s \gamma$ in the vector quark
model. Deviation from the Standard Model arises from the non-unitarity of the
charged current KM matrix and related new FCNC interactions. We establish the
relation between the non-unitarity of charged current mixing matrix and the
mixing among the vector quark and the ordinary quarks. We also make explicitly
the close connection between this non-unitarity and the flavor changing neutral
currents. The complete calculation including leading logarithmic QCD correction
is carefully carried out. Using the most updated data and the NLO theoretical
calculation, the branching fraction of the observed $B$ meson radiative decay
places a limit on the mixing angles as stringent as that from the process $B\to
X \mu\bar\mu$.
