Thermodynamic quantities of the classical He+H-2 mixtures were simulated in the isothermal-isobaric ensemble at T=300 K, P=54 kbar, and several concentrations. The chemical potentials were extrapolated in three directions (T,P,x) with their derivatives calculated by the energy difference method in combination with a modified Kirkwood-Buff fluctuation theory. The phase equilibria at different pressures and temperatures were successfully determined.