Abstract: The difference of three equations of state was studied.It is concluded that Vinet et al.equation of state (EOS) is more compatible with the seismological data than Shanker et al.EOS.Vinet et al.EOS is resemble with the Stacy EOS which consisted with the thermodynamics of high pressure limit and completely compatible with the data derived from seismology.A plot of volume vs.temperature is presented for hcp iron under ICB pressure.The variation of core density deficit with temperature is predicted.The conclusion is important to infer the property of iron in the inner core and deduce the composition of the Earth’s core.