  We apply the background field method to calculate the moments of the pion
two-particles twist-3 distribution amplitude (DA) $\phi_p(\xi)$ in QCD sum
rules. In this paper,we do not use the equation of motion for the quarks inside
the pion since they are not on shell and introduce a new parameter $m_0^p$ to
be determined. We get the parameter $m_0^p\approx1.30GeV$ in this approach. If
assuming the expansion of $\phi_p(\xi)$ in the series in Gegenbauer polynomials
$C_n^{1/2}(\xi)$, one can obtain its approximate expression which can be
determined by its first few moments.
