  In this paper, we verify a part of the Mirror Symmetry Conjecture for
Schoen's Calabi-Yau 3-fold, which is a special complete intersection in a toric
variety. We calculate a part of the prepotential of the A-model Yukawa
couplings of the Calabi-Yau 3-fold directly by means of a theta function and
Dedekind's eta function. This gives infinitely many Gromov-Witten invariants,
and equivalently infinitely many sets of rational curves in the Calabi-Yau
3-fold. Using the toric mirror construction, we also calculate the prepotential
of the B-model Yukawa couplings of the mirror partner. Comparing the expansion
of the B-model prepotential with that of the A-model prepotential, we check a
part of the Mirror Symmetry Conjecture up to a high order.
