Within the framework of the improved isospin dependent quantum molecular dynamics (Im-IQMD) 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 △(1232) and N*(1440). The total pion multiplicities and the π − /π + 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 (ρ/ρ 0 ) γs with γ s = 2. PACS : 25.75.-q, 13.75.Gx, 25.80.Ls Heavy-ion collisions induced by radioactive beam at intermediate energies play a significant role to extract the information of nuclear equation of state (EoS) of isospin asymmetric nuclear matter under extreme conditions. Besides nucleonic observables such as rapidity distribution and flow of free nucleons and light clusters (such as deuteron, triton and alpha etc.), also mesons emitted from the reaction zone can be probes of the hot and dense nuclear matter. The energy per nucleon in the isospin asymmetric nuclear matter is usually expressed as E(ρ, δ) = E(ρ, δ = 0) + E sym (ρ)δ 2 + O(δ 2 ) in terms of baryon density ρ = ρ n + ρ p , relative neutron excess δ = (ρ n − ρ p )/(ρ n +

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A Skyrme-type momentum-dependent nucleon-nucleon force distinguishing isospin effect is parameterized and further implemented in the Lanzhou Quantum Molecular Dynamics (LQMD) model for the first time, which leads to a splitting of nucleon effective mass in nuclear matter.Based on the isospin-and momentum-dependent transport model, we investigate the influence of momentum-dependent symmetry potential on several isospin-sensitive observables in heavy-ion collisions. It is found that symmetry potentials with and without the momentum dependence but corresponding to the same density dependence of the symmetry energy result in different distributions of the observables. The mid-rapidity neutron/proton ratios at high transverse momenta and the excitation functions of the total π − /π + and K 0 /K + yields are particularly sensitive to the momentum dependence of the symmetry potential. PACS : 24.10.Lx, 25.75.-q, 25.70.Pq Keywords: LQMD model; mass splitting; momentum-dependent potential; isospin-sensitive observables; symmetry energy Heavy-ion collisions induced by neutron-rich nuclei at intermediate and relativistic energies in terrestrial laboratories are a useful tool to extract the information of nuclear equation of state (EoS) of isospin asymmetric nuclear matter, which is poorly known for the high-density neutronrich matter but has an important application in astrophysics, such as the structure of neutron star, the cooling of protoneutron stars, the nucleosynthesis during supernova explosion of massive stars etc [1]. The EoS of nuclear matter is usually expressed through the energy per nucleon as * Corresponding author. Tel. +86 931 4969215.