In this paper，free energy method is used to calculate the melting poing of Al. We adopt the Lennard-Jones (LJ) liquid as the reference system and compare the calculated results with that of Mei，Davenport，and Morris et al. The calculated results show: (1) Using the LJ reference system，the CPU-time consumed for molecular dynamics simulation is reduced to one half of that of Mei，Davenport，and Morris et al while the results are the same; (2) Errors exist in calculated values of melting point in all molecular dynamics simulations using different versions of empirical embedded-atom-model potentials (EAM). For the metal Al，the calculated result using Cai's EAM potential is improved a little comparing with that using EAM potentials in the simulations of Mei，Davenport，and Morris et al.