Thermal conductivity of L-J potential solid argon nano-films is calculated by equilibrium molecular dynamics (EMD) and nonequilibrium molecular dynamics (NEMD) simulations in the temperature range from 30K to 80K. A LAMMPS computer program has been modified based on classical molecular dynamics. It can be directly used to calculate the thermal conductivity of nano-films in the direction perpendicular to the film plane. Thermal conductivity calculated from this program is compared with experimental data. It is found that this computer program is competent to calculate the thermal conductivity of solid nano-films. It is also found that thermal conductivity is dependent on the simulation temperature and film thickness.