The effect of anharmonic part is important for understanding the equation of state (EOS) and the thermodynamic properties of cubic iron at the inner core conditions. To incorporate the effects of the anharmonic part, we need to introduce the higher-order anharmonic interactions into the Hamiltonian of lattice dynamical system and the interactions should be directly related to temperature. We realize this by an effective method named self-consistent ab initio lattice dynamics (SCAILD) Souvatzis et al., 2008, in which the phonon-dispersion relations can be obtained at a given temperature and volume. In this method the temperature dependence of phonon frequencies is introduced to simulate the phonon–phonon interactions. However, we must realize that the SCAILD method produces an effective harmonic Hamiltonian, which is a way to approximate the high temperature potential, but as such the method is not exact. Once the phonon dispersion relations are yielded at high temperatures and high pressures, we can obtain the corresponding elastic constants by the long-wave limit approximation without any artificial modification for the effect of temperature.Since we focus on iron properties at inner core, we perform nonmagnetic computations at extreme conditions. More detailed description of the basic theories of present scheme is presented in Section 2.We discuss our results in Section 3. Finally, a summary of our main results is given in Section 4.