  We study the twist-3 distribution amplitudes for scalar mesons made up of two
valence quarks based on QCD sum rules.
  By choosing the proper correlation functions, we derive the moments of the
scalar mesons up to the first two order. Making use of these moments, we then
calculate the first two Gegenbauer coefficients for twist-3 distribution
amplitudes of scalar mesons. It is found that the second Gegenbauer
coefficients of scalar density twist-3 distribution amplitudes for $K^{*}_0$
and $f_0$ mesons are quite close to that for $a_0$, which indicates that the
SU(3) symmetry breaking effect is tiny here. However, this effect could not be
neglected for the forth Gegenbauer coefficients of scalar twist-3 distribution
amplitudes between $a_0$ and $f_0$. Besides, we also observe that the first two
Gegenbauer coefficients corresponding to the tensor current twist-3
distribution amplitudes for all the $a_0$, $K^{*}_0$ and $f_0$ are very small.
The renormalization group evolution of condensates, quark masses, decay
constants and moments are considered in our calculations. As a byproduct, it is
found that the masses for isospin I=1, ${1 \over 2}$ scalar mesons are around
$1.27 \sim 1.41$ GeV and $1.44 \sim 1.56$ GeV respectively, while the mass for
isospin state composed of $\bar{s} s$ is $1.62 \sim 1.73$ GeV.
