  We analyze the exclusive pseudoscalar $D_{[s]}^+D_{[s]}^-$ pair production in
$e^+e^-$ annihilations at $\sqrt{s}=10.6$ GeV using a non-factorized PQCD with
the light-front wave function that goes beyond the peaking approximation. We
compare our non-factorized analysis with the usual factorized analysis based on
the peaking approximation in the calculation of the cross section for the heavy
meson pair production. We also discuss the higher helicity contribution to the
cross section. Our analysis provides a constraint on the size of quark
transverse momentum inside the $D$ meson from the recent Belle data,
$\sigma_{\rm Exp.}(e^+e^-\to D^+D^-)<0.04$.
