The molecular dynamics method combined with simulated annealing technique was performed to investigate the structures and size-dependent melting of gold nanocluster.In our study,the Reaxff gold force field [1,2] was applied.Our annealing results show that the icosahedron structure of 55-atom is more stable than cuboctahedron structure.For the other nanoclusters of Aun(n=309(1.2nm),923(2.4nm),2057(3.3nm),3871(4.1nm)),the well-ordered initial structures become amorphous at high temperature,the melting point of studied nanoclusters are obtained.Over the course of the annealing procedure,we find that the nanocluster can relax into a different structure when cooled.We find that the larger nanoparticles correspond to the higher metling temperature.