Phase diagram of a Lennard-Jones fluid at liquid-gas equilibrium is studied by molecular dynamics simulations. The problem of potential cut-off influence on the properties of the model system is investigated. For several values of the cut-off radius, the physical properties of coexisting phases and critical parameters are calculated. It is shown that the results obtained for various cut-offs scaled by the critical temperature and density coincide, which means that fluids described by different modifications of the Lennard-Jones potential are thermodynamically similar, i.e., obey a corresponding states law.