  The derived modular invariant one-loop string effective coupling constant has
been used to discuss the weak scale measurement constraints on minimal
superstring models, minimal SUSY left-right string models and minimal
left-right SUSY string models. The string intermediate gauge symmetry breaking
models are proposed. The possible schemes to predict $M_{GUT} = 10^{16}GeV$ and
$M_{SUSY}= 1 TeV$ in string models have been discussed. It is also demonstrated
that string unification is more restricted by the experiments than any other
unification models are.
