  Because of the problems arising from the fermion unification in the
traditional Grand Unified Theory and the mass hierarchy between the
4-dimensional Planck scale and weak scale, we suggest the low energy gauge
unification theory with low high-dimensional Planck scale. We discuss the
non-supersymmetric SU(5) model on $M^4\times S^1/Z_2 \times S^1/Z_2$ and the
supersymmetric SU(5) model on $M^4\times S^1/(Z_2\times Z_2') \times
S^1/(Z_2\times Z_2')$. The SU(5) gauge symmetry is broken by the orbifold
projection for the zero modes, and the gauge unification is accelerated due to
the SU(5) asymmetric light KK states. In our models, we forbid the proton
decay, still keep the charge quantization, and automatically solve the fermion
mass problem. We also comment on the anomaly cancellation and other possible
scenarios for low energy gauge unification.
