  Within the framework of the improved isospin dependent quantum molecular
dynamics (ImIQMD) model, the emission of pion in heavy-ion collisions in the
region 1 A GeV as a probe of nuclear symmetry energy at supra-saturation
densities is investigated systematically, in which the pion is considered to be
mainly produced by the decay of resonances $\triangle$(1232) and N*(1440). The
total pion multiplicities and the $\pi^{-}/\pi^{+}$ yields are calculated for
selected Skyrme parameters SkP, SLy6, Ska and SIII, and also for the cases of
different stiffness of symmetry energy with the parameter SLy6. Preliminary
results compared with the measured data by the FOPI collaboration favor a hard
symmetry energy of the potential term proportional to
$(\rho/\rho_{0})^{\gamma_{s}}$ with $\gamma_{s}=2$.
