  We investigate a 6d generalized Randall-Sundrum brane world scenario with a
bulk cosmological constant. It is shown that each stress-energy tensor
$T_{ab}^{i}$ on the brane is similar to a constant vacuum energy. This is
consistent with the Randall-Sundrum model in which each 3-brane Lagrangian
separated out a constant vacuum energy. By adopting an anisotropic metric
ansatz, we obtain the 5d Friedmann-Robertson-Walker field equations. At a
little later period, the expansion of the universe is proportional to
$t^{\frac{1}{2}}$ which is as similar as the period of the radiation-dominated.
We also investigate the case with two $a(t)$ and two $b(t)$. In a large region
of $t$, we obtain the 3d effective cosmological constant
$\Lambda_{eff}=-2\Omega/3>0$ which is independent of the integral constant.
Here the scale factor is exponential expansion which is consistent with our
present observation of the universe. Our results demonstrate that it is
possible to construct a model which solves the dark energy problem, meanwhile
guaranteeing a positive brane tension.
