  Applying effective Lagrangian method and on-shell scheme, we analyze the
electroweak corrections to the rare decay $b\rightarrow s+\gamma$ from some
special two loop diagrams in which a closed heavy fermion loop is attached to
the virtual charged gauge bosons or Higgs. At the decoupling limit where the
virtual fermions in inner loop are much heavier than the electroweak scale, we
verify the final results satisfying the decoupling theorem explicitly when the
interactions among Higgs and heavy fermions do not contain the nondecoupling
couplings. Adopting the universal assumptions on the relevant couplings and
mass spectrum of new physics, we find that the relative corrections from those
two loop diagrams to the SM theoretical prediction on the branching ratio of
$B\rightarrow X_{_s}\gamma$ can reach 5% as the energy scale of new physics
$\Lambda_{_{\rm NP}}=200$ GeV.
