  We study the pion leading-twist distribution amplitude (DA) within the
framework of SVZ sum rules under the background field theory. To improve the
accuracy of the sum rules, we expand both the quark propagator and the vertex
$(z\cdot \tensor{D})^n$ of the correlator up to dimension-six operators in the
background field theory. The sum rules for the pion DA moments are obtained, in
which all condensates up to dimension-six have been taken into consideration.
Using the sum rules, we obtain $\left<\xi^2\right>|_{\rm 1\;GeV} = 0.338 \pm
0.032$, $\left<\xi^4\right>|_{\rm 1\;GeV} = 0.211 \pm 0.030$ and
$\left<\xi^6\right>|_{\rm 1\;GeV} = 0.163 \pm 0.030$. It is shown that the
dimension-six condensates shall provide sizable contributions to the pion DA
moments. We show that the first Gegenbauer moment of the pion leading-twist DA
is $a^\pi_2|_{\rm 1\;GeV} = 0.403 \pm 0.093$, which is consistent with those
obtained in the literature within errors but prefers a larger central value as
indicated by lattice QCD predictions.
