  We propose low energy 6-dimensional N=2 supersymmetric SU(6) models on
$M^4\times T^2/(Z_2)^3$ and $M^4\times T^2/(Z_2)^4$, where the orbifold
$SU(3)_C\times SU(3)$ model can be embedded on the boundary 4-brane. For the
zero modes, the 6-dimensional N=2 supersymmetry and the SU(6) gauge symmetry
are broken down to the 4-dimensional N=1 supersymmetry and the $SU(3)_C\times
SU(2)_L\times U(1)_Y\times U(1)'$ gauge symmetry by orbifold projections. In
order to cancel the anomalies involving at least one $U(1)'$, we add extra
exotic particles. We also study the anomaly free conditions and present some
anomaly free models. The gauge coupling unification can be achieved at $100\sim
200$ TeV if the compactification scale for the fifth dimension is $3\sim 4$
TeV. The proton decay problem can be avoided by putting the quarks and
leptons/neutrinos on different 3-branes. And we discuss how to break the
$SU(3)_C\times SU(2)_L\times U(1)_Y\times U(1)'$ gauge symmetry, solve the
$\mu$ problem, and generate the $Z-Z'$ mass hierarchy naturally by using the
geometry. The masses of exotic particles can be at the order of 1 TeV after the
gauge symmetry breaking. We also forbid the dimension-5 operators for the
neutrino masses by $U(1)'$ gauge symmetry, and the realistic left-handed
neutrino masses can be obtained via non-renormalizable terms.
