When molecular dynamics method is used to simulate femtosecond laser ablation of aluminum (Al) in argon (Ar) environment, the interaction of Ar and Al atoms needs to be considered. The potential function of Ar-Al interaction is obtained by combining two types of potential functions, including short range and long range. The molecular dynamics simulation results of femtosecond laser ablation at corresponding small system and scale are given by using the interaction potential. Ziegler-Biersack-Littmark (ZBL) potential function is used in shorter range of Ar-Al interatomic potential. Lennard-Jones (LJ) potential function is used in longer range. Second-order polynomial is used at the intermediate distance. The parameters of LJ potential function are obtained by fitting the Ar-Al binding energy. The Ar-Al interatomic potential function is used in molecular dynamics simulation of femtosecond laser ablation of aluminum in argon environment. The ablation dynamic images under picosecond time delay and the evolution laws of temperature and density of Ar in the process are obtained.