The molecular dynamic simulation was performed on the homogenous nucleation of argon vapor,and the nucleation rate was calculated by classic nucleation theory(CNT),mean first-passage times(MFPT),and cluster theory,respectively.The simulation results show that under the same simulation condition,the nucleation rates calculated by the MFPT and the cluster theory are of the same order of magnitude,and are of three orders of magnitude higher than those calculated by the CNT theory because of the equilibrium thermodynamics assumption with the CNT theory.Moreover,the critical cluster number of homogenous nucleation for the three methods is close to 20.In addition,from the cluster theory analysis,the nucleation rate increases with the increase in the cooling rate,which agrees well with practical homogeneous nucleation.