  Isospin symmetry, as the most precise flavor symmetry, could be used to
extract information of hadronic dynamics. The effective Hamiltonian of bottom
quark weak decay is zero under the isospin lowering operators $I_-^n$, which
permits us to generate isospin sum rules through several master formulas. In
this work, we derive the master formulas of isospin sum rules for the two- and
three-body non-leptonic decays of $B$ mesons. The isospin sum rules can be used
to test of isospin symmetry and provide hints the isospin partners of exotic
hadrons in the $B$ decays. It is found the isospin breaking could reach to be
$\mathcal{O}(10\%)$ in some decay modes. And the charm tetraquark resonances
might be observed in the $ B^- \to J/\Psi \pi^-\overline K^0$, $\overline B^0
\to J/\Psi \overline K^0\phi$ and $\overline B^0\to D^0\overline D^0\overline
K^0$ modes according to the isospin symmetry.
