  Within the framework of the isospin-dependent
Boltzmann-Uehling-Uhlenbeck(IBUU) transport model, we studied the effects of
the pion potential and the symmetry energy on the pion production in the
central $^{197}Au+^{197}Au$ collisions around the pion production threshold. It
is found that the pion potential has opposite effects on the value of
$\pi^-/\pi^+$ ratio at low and high pion energies. The effect of the pion
potential on the total $\pi^-/\pi^+$ ratio becomes larger in heavy-ion
collisions at beam energies below the pion production threshold. And at beam
energies below the pion production threshold, with the pion potential, the
effect of the symmetry energy on the $\pi^-/\pi^+$ ratio becomes smaller
compared with that above the pion production threshold.
