Method of molecular dynamics has been proposed which exhibits the development of films damage from micro angle in virtue of computer in detail. It can make the development of damage more visualized which cannot be observed in experiment. With Lennard-Jones potential function, pre-correct integrates method and dummy-force-restrict-demarcate method are used. The effect of the density and temperature of the films on the thermal conductivity is simulated. With the radial distribution function and long distance distribution function, the structure characteristics of system have been analyzed. Besides, the high-temperature-size-effect has been studied by using different simulating sizes. The results show that the thermal conductivity increases when density or temperature increases which cannot be obtained from experimental methods. This kind of simulation can provide some useful data for research.