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.
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