  We study the path from the string scale physics to the low-energy physics in
the $SU(6) \times SU(2)_R$ string-inspired model with the flavor symmetry ${\bf
Z}_M \times {\bf Z}_N \times \tilde{D}_4$. The flavor symmetry controls the
mass spectra of heavy particles as well as those of quarks and leptons in the
intermediate energy region ranging from the string scale ($\sim 10^{18} {\rm
GeV}$) to the electroweak scale. In this paper we examine the mass spectra of
heavy particles in detail in our model. The renormalization group evolution of
the gauge couplings is studied up to two-loop order. A consistent solution of
the gauge unification around the string scale is found by adjusting the spectra
of the anti-generation matter fields.
