Let
X
X
be a Kähler manifold which is fibered over a complex manifold
Y
Y
such that every fiber is a Calabi-Yau manifold. Let
ω
\omega
be a fixed Kähler form on
X
X
. By Yau’s theorem, there exists a unique Ricci-flat Kähler form
ω
K
E
,
y
\omega _{KE,y}
on each fiber
X
y
X_y
for
y
∈
Y
y\in Y
which is cohomologous to
ω
|
X
y
\omega \vert _{X_y}
. This family of Ricci-flat Kähler forms
ω
K
E
,
y
\omega _{KE,y}
induces a smooth
(
1
,
1
)
(1,1)
-form
ρ
\rho
on
X
X
under a normalization condition. In this paper, we prove that the direct image of
ρ
n
+
1
\rho ^{n+1}
is positive on the base
Y
Y
. We also discuss several byproducts including the local triviality of families of Calabi-Yau manifolds.