  Based on the generalized gauge theory on $M^4\times Z_2\times Z_3$, we
reconstructed the realistic SU(5) Grand Unified model by a suitable assignment
of fermion fields. The action of group elements $Z_2$ on fermion fields is the
charge conjugation while the action of $Z_3$ elements represent generation
translation. We find that to fit the spontaneous symmetry breaking and gauge
hierarchy of SU(5) model a linear term of curvature has to be introduced. A new
mass relation is obtained in our reconstructed model.
