  The three-body decay $B^0(B_s)\to \gamma\nu \bar{\nu}$ can occur via penguin
and box diagrams in the standard model (SM). These channels are useful to
determine the decay constants $f_B$ ($f_{B_s}$) and $B$ ($B_s$) meson wave
function. Using the B meson wave function determined in hadronic $B (B_s)$
decays, we calculate and get the branching ratio of order $10^{-9}$ and
$10^{-8}$ for $B^0$ and $B_s$ decay, respectively. They agree with previous
calculations.
