By combination of an equation-of-state (EOS) theory and molecular simulation methods, a new way to predict and to analyze the surface phenomena of polymeric materials is suggested. The EOS parameters, p*, v(sp)* and T* of polyethylene are calculated by molecular simulation methods, without any experimental effort. With the calculated parameters, surface tensions and density profiles at surface are obtained by numerically integrating Poser and Sanchez’s equations. The calculated surface tensions without adjustable parameters are slightly underestimated as compared to the experimental measurements. The underestimation may come from the fact that the simulated densities are lower than the experiments and that the EOS parameters are practically functions of temperature.