It has remained an open problem to accurately compute the partition function of macroscopic systems since the establishment of statistical physics.A rapid method approaching this problem was presented and was strictly tested by molecular dynamic (MD) simulations on Ar atoms in both dense gaseous and liquid states.The outcomes from the method on the inteal energy and the work of isothermal expansion (and therefore the free energy) are in good agreement with the MD simulations,suggesting the method would be immediately applied in vast areas.